Cluster Management Service

Configuration Reference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

21-October-2016

Andrew Hanushevsky

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

XRootD: Structured Cluster Architecture for Low Latency Access

©2003-2016 by the Board of Trustees of the Leland Stanford, Jr., University

All Rights Reserved

Produced under contract DE-AC02-76-SFO0515 with the Department of Energy

This code is open-sourced under a GNU Lesser General Public license.

For LGPL terms and conditions see http://www.gnu.org/licenses/


1       Introduction. 5

1.1        Directives and Components. 9

1.1.1     Clusters with 64 or fewer data servers. 9

1.1.2     Clusters with 65 or more data servers. 11

1.1.3     Frequently asked questions. 14

1.3        Starting the cmsd Process. 17

1.3.1     Multiple Instances and Automatic Fencing. 22

1.3.2     Log File Plug-Ins. 23

1.3.3     Files created by cmsd. 24

1.3.4     Exported Environment Variables. 26

2       Mandatory Configuration Directives. 27

2.1        manager. 27

2.1.1     Choosing all vs. any for Normal Managers. 29

2.1.2     Peer Manager File Location and Selection. 30

2.1.3     Disjoint Cluster Configurations. 31

2.2        role. 33

2.2.1     Role Summary Table. 34

3       Common Configuration Directives. 37

3.1        adminpath. 37

3.2        allow.. 38

3.3        defaults (an oss directive) 39

3.4        dfs. 41

3.5        export 45

3.6        localroot (an oss directive) 47

3.7        perf 48

3.8        prep. 51

3.8.1     Optional Prepare Interface Program Requirements. 53

3.9        sched. 57

3.10     seclib. 61

3.11     space. 62

3.12     space (an oss directive) 64

4       Esoteric Configuration Directives. 65

4.1        altds. 65

4.2        blacklist 66

4.3        cidtag. 68

4.4        conwait 69

4.5        delay. 71

4.5.1     Relationship Between hold & lookup Delay vs. qdl 75

4.6        fxhold. 76

4.7        fsxeq. 77

4.8        namelib (an oss directive) 79

4.9        nowait 80

4.10     osslib (an ofs directive) 81

4.11     pidpath. 82

4.12     ping. 83

4.13     prepmsg. 85

4.14     remoteroot (an oss directive) 87

4.15     repstats. 88

4.16     request 89

4.17     subcluster. 90

4.18     trace. 91

4.19     whitelist 93

5       Blacklist and Whitelist File Format 95

6       The Composite Cluster Name Space. 97

6.1        Establishing a Composite Name Space. 97

6.1.1     Frequently asked questions. 100

6.2        Maintaining a Simple Server Inventory. 101

6.3        XrdCnsd Program.. 103

6.3.1     Created Files. 107

6.4        Listing Differences with cns_ssi diff 109

6.5        Listing the inventory with cns_ssi list 111

6.6        Updating the inventory with cns_ssi updt 113

7       Document Change History. 115


1        Introduction

 

This document describes Cluster Management Service Distributed configuration directives. This component provides dynamic load balancing of files and name-space consolidation of distributed data regardless of location. The cms component is meant to be used with xrootd’s Open File System (ofs) component. Refer to the “xrootd ofs & oss Configuration Guide” for detailed information.

 

Directives for cmsd, the clustering daemon and its client counterpart used by the ofs component, come from a configuration file. The characters “cms” must prefix each directive in the configuration file. Directives that apply to multiple components must be preceded by the characters “all”. This makes cms directives compatible with the xrootd’s other configurable components:

 

Component

Purpose

acc

Access control (i.e., authorization)

cms

Cluster Management Service

ofs

Open file system coordinating acc, cms, & oss components

oss

Open storage system[1] (i.e., file system implementation)

sec

Security authentication

xrd

Extended request daemon.

xrootd

xrootd protocol.

all

Applies the directive to all of the above components.

 

Records that do not start with a recognized identifier are ignored. This includes blank record and comment lines (i.e., lines starting with a pound sign, #). This guide documents the all and cms configuration directives (i.e., the un-shaded rows). Other directives are documented in supplemental guide specific to the component they deal with.

 

The location of the configuration file is specified on the command line. Because each component has a unique prefix, a common configuration file can be used for the whole system.

 

Refer to the manual “Configuration File Syntax” on how to specify and use conditional directives and set variables. These features are indispensable for complex configuration files usually encountered in large installations.

 

A configuration file is mandatory, even if nothing is specified in it. Because load balancing is sensitive to other configuration options, the cmsd does recognize certain specific directives that start with the oss prefix. This allows the use of a single configuration file without the need to duplicate directives. The cms prefix, applies directives specifically to the Cluster Management Service and no other component. Additionally, directives prefixed by “all” also apply to the Cluster Management Service. 

 

Clustering is performed by a set of cooperating servers. One or more cmsd daemons run in manager mode and can be used by one or more xrootd’s to determine where to redirect a client’s file open request. The request can only be redirected to a machine that is running a cmsd in server or supervisor mode. There can be up to 64 cmsd servers. Each machine can run one or more xrootd’s. The following figure illustrates a simple minimal system.

 

Text Box:  
Figure 1.1.1 1: Client-Server Clustering Dynamics

 

In the diagram, there are three hosts: x, y, and z. Host y serves as the load balancer. Hosts x and z are the hosts that can be used to serve data to clients and load is to be distributed between the two. Consequently, host y runs a manager cmsd while hosts x and z run server cmsd’s.

The servers connect to the manager and provide load information. The xrootd running on host y connects to the manager as well. However, the xrootd on host y uses the manager to determine which server to direct client requests. It does not serve any actual data files.

 

The typical open request is handled in four steps:

1.               The client directs the open request to the xrootd that runs on the manager’s host.

2.               The xrootd asks the cmsd manager which machine is the best to use to process the file. The manager determines the best machine using a variety of configurable parameters.

3.               The xrootd on host y tells the client, in this example, that host z is the best host to use for the file.

4.               The client then redirects the request to the xrootd running on host z.

 

In order to make the system as flexible as possible, the manager cmsd does not know how many or which hosts will acts as servers. For security purposes, you can restrict hosts based on host name as well as by NIS netgroup. Thus, servers essentially subscribe to the manager claiming that they have file resources. During the subscription process, each server indicates the file paths to which it is willing to provide data access. Periodically, the manager cmsd requests load information from each server. Each server reports CPU, network I/O, queue, memory, paging load as well as free space. This information is used to select the best available server for an open request.

 

The decision is tempered whether or not the server already has the file on disk or whether the file must be staged to disk from a Mass Storage System. The manager may decide that all available servers are too loaded and force a file to be replicated on a less loaded server. This provides additional data paths to the file. Replicated load balancing is only compatible with read-only files. The manager can direct client’s to a writable version of a files but only on servers that have indicated that they offer write access on the associated path. In general, only one such server may exist for each particular path.

 

In order to provide a fully redundant service, all servers may be replicated and cross-connected. The following figure shows a full crossbar configuration.

Each server cmsd subscribes to two manager cmsd’s. Each xrootd that can redirect clients subscribes to two managers. Thus, the loss of any single manager xrootd does not affect load balancing. More complex arrangements are possible since each server may have any number of managers and each xrootd can subscribe to any number of managers.

 

In order to ease migration, any peripheral (i.e., data server) xrootd can always be directly used[2]. This means that load balancing only occurs when a client contacts a redirecting xrootd. For systems that are being configured this way for the very first time, you should always use the xrd.port any” directive for data server xrootd’s. This allows the xrootd to use an arbitrary port number. In this mode it is very difficult for any client to directly use a data server xrootd without first contacting the manager xrootd first.

 Text Box:  
 Figure 1.1.1 2: A Fully Redundant Cluster Configuration


1.1      Directives and Components

 

Clustering consists of four distinct components:

1.     The manager cmsd process (typically in a separate machine).

2.     Supervisor cmsd processes (only for clusters of more than 64 servers).

3.     Server cmsd processes, and

4.     An integrated cmsd client in the xrootd process, which can be a manager, supervisor, or server.

 

A manager cmsd always communicates with supervisor and server cmsd’s as well as a manager xrootd. Server xrootd’s only communicate only component with their  server cmsd counterpart. Two distinct directives are used to identify the participants:

1. all.role which tells each component whether it is to function as a manager, supervisor, or server; and

2. all.manager that tells each component the DNS name of the manager.

1.1.1       Clusters with 64 or fewer data servers

Use the following general steps to successfully configure a cluster that has 64 or fewer data servers:

  • Determine which servers will be used for data serving (i.e., run a data server cmsd) and which for redirection (i.e., run a manager cmsd). A manager is not capable of also serving data. Use the “all.role” directive to differentiate servers and managers.
  • Use the allow directive to restrict the set of valid data servers.
  • Determine the scheduling policy using the cms.sched and cms.space directives.
  • Determine which port number will be used for inter-server communication and specify it for the manager cmsd using the mandatory all.manager directive (see below).
  • Remember to specify the xrootd port number for the associated manager xrootd using the xrd.port directive, if the default of 1094 is unacceptable.
  • Determine the set of data servers. Unless direct access is important, you should configure data servers with “xrd.port any”.
  • For each data server, determine which file paths it will handle. In general, a number of servers should serve the same path.
  • Use the all.export directive on each data server to restrict it to its set of paths.
  • If a data server will be also creating files, use the space directive to indicate which file systems may be used for file creation.
  • Use the all.manager directive to tell each xrootd and cmsd the location of its set of managers.
  • Start a data server cmsd server on each xrootd data server machine. For each xrootd that will be redirecting, use the all.role manager directive to enable redirection mode.[3]
  • Start the manager, server, and xrootd. See the cmsd command described in the next section. The start-up order is not important.

 

The following diagram and corresponding configuration file illustrates how to cluster 30 data servers with two managers.

 

 

# Specify the data server port number. This is only relevant to

# managers, so we qualify the specific port number using the “if”.

#

xrd.port any

xrd.port 1094 if man01.u.org man02.u.org

 

# Specify which paths are to be exported (default is r/w)

#

all.export /data

 

# Tell everyone the role it will have. Use a default of server but

# qualify it depending on hostname using the “if”.

#

all.role server

all.role manager if man01.u.org man02.u.org

 

# Tell everyone the location of each manager.

#

all.manager man01.u.org:1213

all.manager man02.u.org:1213

 

# Tell the cmsd which machines are allowed to connect

#

cms.allow host man*.u.org

cms.allow host data*.u.org

 

 

Configuration “myconfig.cf” for a 30 Data Server Cluster

 

There are additional directives to further tune the system and are described on the following pages.


1.1.2       Clusters with 65 or more data servers

Configuring a cluster of more than 64 data servers is just slightly more complicated than configuring a smaller cluster. The complication arises from the fact that some additional management servers need to be started. The configuration file, however, is no more complicated. Below are the steps you should take to successfully configure large clusters.

 

  • Choose the port numbers you wish to use for the manager xrootd and cmsd servers. Typically, xrootd uses port 1094 and specified with the xrd.port directive. For cmsd port 1213 is used and specified with the all.manager directive. Other xrootd servers should specify “xrd.port any”.
  • Choose the number of manager nodes you wish to run. You must configure at least one manager node. The manager is the first point of contact for a client and is also the cluster leader. A manager should run on a dedicated machine of modest power (e.g., 512MB RAM, 800MHZ clock speed, 100Mb ethernet).

 

A manager node consists of

a)     an xrootd configured with the “all.role manager” directive.

b)    a cmsd configured with “all.role manager” directive.

 

You may configure more than one manager and run them in either fail-over mode (the default) or in load balancing mode where each manager shares part of the client load (see the all.manager directive). Each manager xrootd-cmsd pair must run on a separate machine.

  • Compute the number of supervisor nodes you need. A supervisor node acts as a local manager for a group of 64 other nodes. These nodes may be data servers or supervisors. A supervisor node consists of

a)     an xrootd configured with the “all.role supervisor” directive. Additionally, specify the “xrd.port any” directive.

b)    a cmsd configured with the “all.role supervisor” directive.

 

You only need to configure supervisor nodes if you are running more than 64 data servers. The number of supervisor nodes is based on the number of available manager plus supervisor slots. A recursive formula is needed to calculate the minimum number. Since you normally wish to start more than the minimum number of supervisors, a simplified formula can be used.

 

Conservatively, you will need one supervisor node for each group of 64 data servers. For instance, if you plan to run 500 data servers you will need the upper limit of 500/64 supervisors (i.e., 8).

 

Each supervisor node can run on a data server node. If you wish to share resources in this way, choose data server nodes that will be as lightly loaded as possible. The performance requirements for a supervisor node are the same as a manager node.

  • Configure the data server nodes. A data server node delivers actual data to clients. It consists of

a)     an xrootd configured with the “all.role server” directive. Additionally, specify the “xrd.port any” directive.

b)    a cmsd configured with the “all.role server” directive.

 

Configure as many data server nodes as you need. Keep in mind that at least one additional supervisor node is need for each group of 64 data servers.

 

The performance requirements are determined by the performance needs of clients. The server should have enough disk space, adequate network bandwidth (e.g., Gb ethernet), and significant cpu and i/o resources. If you wish to use memory mapped files, then the node should have a commensurate amount of real memory.

 

For example, assume you wish to cluster 99 data servers in the way shown below.

Here we wish to have only one manager. We will need at least one supervisor. While the simplistic formula indicates two supervisors are needed; in practice, the cluster could self-organize by affiliating 63 data servers and one supervisor (a total of 64) with the manager and affiliating the remaining data servers (36) with the supervisor.

With two supervisors, the cluster would affiliate 62 data servers and two supervisors with the manager, and split the remaining data servers across the two supervisors. So, either configuration would work. Fortunately, the cluster attempts to automatically find the best organization given the resources at hand. Configuration files for small and large clusters will differ only slightly from each other. Notable differences involve allow and role directives. Configuration file simplicity relies on the use of regular names for various hosts.

 

 

# Specify the data server port number. This is only relevant to

# managers, so we qualify the actual port number using the “if”.

#

xrd.port any

xrd.port 1094 if man01.u.org

 

# Specify which paths are to be exported (default is r/w)

#

all.export /data

 

# Tell the cmsd which machines are allowed to connect

#

cms.allow host man01.u.org

cms.allow host sup01.u.org

cms.allow host data*.u.org

 

# Indicate the role this server will have based on host name (the

# default role is that of server)

#

all.role server

all.role supervisor if sup01.u.org

all.role manager    if man01.u.org

 

# Tell everyone the location of the manager.

#

all.manager man01.u.org:1213

 

Configuration “myconfig.cf” for a 99 Data Server Cluster

 


1.1.3       Frequently asked questions

 

Does start-up order matter?

Generally, it does not matter in which order nodes are started. For the efficiency minded, starting supervisor nodes ahead of data server nodes allows the system to converge on a stable configuration faster.

 

How long will it take for the system to converge?

This depends on how many servers are in the configuration. Generally, it takes approximately 1 to 13 seconds for a server to find its correct place in the cluster. However, the process is run in parallel across all of the servers. So, the system should converge in less than 30 seconds for a configuration of about a 1,000 nodes. By default, the system delays full availability for 90 seconds, this should be sufficient time for convergence of even extremely large installations.

 

What happens if I have too few supervisors?

If there are not enough supervisors relative to the number of data servers, one or more data servers will be orphaned and unavailable. If you suspect this, check the manager’s log. It will contain warnings about orphaned data servers.

 

What happens if I have more supervisor nodes than I need?

Since the system tries to evenly distribute data servers across all available supervisors, excess supervisors are used to further reduce the load on supervisor nodes. The excess supervisors are also used as “hot spares” in the event one of the supervisors becomes unavailable. You should configure as many “extra” supervisors as you feel are necessary to provide a suitable level of fault tolerance.

 

Can I run all the supervisors on a single node?

Yes, but you will need to assign each cmsd a unique instance name using the –n option. Additionally, the same –n option value must be specified for the xrootd that is paired with a particular cmsd. Use the “if” directive, keyed off the instance name, to maintain a single configuration file. Finally, each xrootd, other than the one tied to the manager cmsd, must be started with the “port any” directive to allow for arbitrary port selection. You should realize that running all of the supervisors on a single node creates a large single point of failure.


How do I run a data server and a supervisor on the same node?

Use the provided StartCMS and StartXRD scripts. For a supervisor cmsd and xrootd, specify the “all.role supervisor”. For a data server cmsd and xrootd specify the “all.role server” directive. You should make sure that “xrd.port any” is specified for supervisor and data server xrootd’s to prevent any port conflicts

 

What does the “–port any” xrootd command line option actually do?

The “-port any” option allows xrootd to choose any port that is available. The selected port number is then forwarded to the cmsd. This allows the cmsd to redirect clients to the proper port even though it’s not known ahead of time. This only works if the cmsd is not started with the -i option (the default) and the xrootd is started with the all.role server” (for data servers) or all.role supervisor” directive (for supervisors). This does not eliminate the need for starting the manager cmsd and its xrootd counterpart with well-known ports

 

Does that mean I can use –port any to run multiple data servers on a single node?

Yes. See the answer to “Can I run all the supervisors on a single node?

 

Can I use the –port any option to prohibit clients to bypass the cmsd?

Yes. This is actually recommended. Since arbitrary port numbers are chosen, a client cannot directly connect to a data server without using the manager xrootd. However, while significant programming effort is required to capture port numbers at run-time; any “management by obscurity” method can be defeated.



1.3      Starting the cmsd Process

 

Use the following command to start a manager or server cmsd process.

 

 

cmsd  -c cfn [-l largs] [-k {num | sz{k|m|g} | sig}]

 

         [esoteric]

 

largs:     [=]fn | - |

           @lib[,bsz=sz][,cse={0|1|2}][,logfn=[=]fn]

 

esoteric: [-b] [-d] [-i] [-I {v4 | v6}] [-n name]

 

          [-p port] [-s pfn] [-S site] [-z]

 

sig:      fifo|hup|rtmin|rtmin+1|rtmin+2|ttou|winch|xfsz

 

 

Parameters

-c cfn   The name of the configuration file. You must specify the name of a configuration file even if it is empty.

 

Options

-l  largs          

Specifies how messages are to be handled. Options are:

fn         Directs messages and any trace output to the indicated file, fn, possibly qualified by the instance name (see the fencing section). By default, messages are directed to standard error.

=fn       Same as fn but the fn is not qualified by the instance name, if any. This allows log files to be handled in an arbitrary manual way. For more information see the section on fencing.

@lib     Directs messages to a plug-in that is defined in the shared library specified by lib (see the section on log file plug-ins). Additional comma-separated parameters may follow lib, as follows:

bsz=sz            Specifies the size of the speed matching buffer. The default is 64K.  Messages are placed in the buffer and then forwarded to the plug-in as time permits. A value of 0 disables speed matching and messages are handed off to the plug-in as they occur. See the section on log file plug-ins for more information. A positive value less than 8K is forced to be 8K. The maximum allowed in one megabyte. The sz may be suffixed by k or m to indicate kilobytes or megabyte, respectively.

cse={0|1|2}    Specifies how standard error output should be handled:

0       Does not capture standard error output. All such output is sent to the logfn destination, if specified, or is otherwise lost. This is the default.

1       Captures standard error but only forwards it to the logging plug-in if it starts with a standard time stamp. This option may cause an infinite loop. Refer to the logging plug-in section for more information.

2       Captures standard error output and forwards it to the logging plug-in without inspection.  Refer to the logging plug-in section for more information.

logfn=[=]fn    Specifies that messages are also to be routed to a local log file. The parameter is identical to that described above. To use standard error, specify a dash (-) for fn.

 

-k num | sz{k|m|g} | sig

Keep no more than num old log files. If sz is specified, the number of log files kept (excluding the current log file) is trimmed to not exceed sz bytes. The sz must be suffixed by k, m, or g to indicate kilobytes, megabyte, or gigbytes, respectively. If a sig value is specified (i.e. hup etc), then an external program is expected to handle log file rotation (e.g. logrotate). Except for fifo, the argument specifies signal that causes the daemon to close and re-open the log file to allow rotation to occur. When fifo is specified, the daemon waits for data to appear on a fifo whose path is identical to the log file path but whose name is prefixed by a dot. Refer to the notes for manual rotation caveats.

 

 

Esoteric Options

-b        Runs the program in the background. You should also specify -l.

 

-d        Turns on debugging.

 

-i         The cmsd subscribes to a manager cmsd whether or not the local primary data server contacts the cmsd. Also, see the cms.nowait directive.

 


 

-I {v4 | v6}

            Restricts the server’s internet address protocol. When v4 is specified, only hosts with IPV4 addresses can connect or be connected to. When v6 is specified, the default, hosts using IPV6 or IPV4 addresses can connect or be connected to. This option is only useful for systems that have misbehaving IPV6 network stacks. The default is established by the network interface configuration on the machine at the time the program starts.

 

-n name         

The instance name of the cmsd. There is no default. See the notes for more information on this option.

 

-p port

The TCP port, or service name associated with a port, that the manager cmsd is to use for new connections. There is no default. If the port is not specified on the command line, it must be specified using the all.manger directive.

 

-s pfn  Specifies the name of the file that is to hold the process id upon start-up.

 

-S site Specifies a 1- to 15-character site name that is to be included in monitoring records. The name may only contain letters, digits and the symbols “_-:.”; any other characters are converted to a period.

 

-z         provides microsecond resolution for log file message timestamps.

 

Defaults

cmsd –l - –I v.

 

Notes

1)     A configuration file is not optional.

2)     The same configuration file may be used for manager and server cmsd’s. Directives not relevant to a particular mode of operation are ignored.

3)     The cmsd related directives may be placed in the xrootd configuration file as well. Thus only one configuration file needs to be maintained per machine.

4)     The order in which servers are started is unimportant.


 

5)     When a signal value is specified, log files are not automatically renamed at midnight. Instead an external program must be used to properly rotate log files. Make sure to choose a signal that is not in use by any plug-in. If unsure, choose one of the obscure signal names and monitor for any odd behavior. Otherwise, use the fifo option. Be aware that on some non-Linux platforms the fifo file descriptor may leak.

6)     When fifo is specified the fifo file name must not exists or exist as a fifo file. A simple “echo x >> /path/.lfn” causes the logfile to close and reopen.

7)     The sig names, except for fifo, be fully capitalized as well prefixed by “sig” or “SIG” when capitalized.

8)     You must start at least one cmsd in manager mode. The number of supervisor cmsd’s is approximately determined by dividing the number of server mode cmsd’s by 64 less one.

9)     In a supervisor role, the cmsd acts as both manager and server. Supervisor cmsd’s are used to cluster groups of 64 server cmsd. Since a supervisor cmsd can subscribe to a manager or supervisor cmsd, it is possible to cluster together a virtually unlimited number of data servers.

10) During start-up, a cmsd writes its process id as well as its local path prefix and administrative path into a file. The location of the file is determined by the pidpath directive, as modified by the –n option. The name of the file is determined by the cmsd’s role (see the role directive). Refer to the section “Created Files” for the name used for this file.

 

Notes on Esoteric Options

1)     The –i option provides for a loose coupling between servers running on the same host. The cmsd executes asynchronously from the host’s data server and can subscribe to a manager before the data server is available on the host.

2)     Without –i, a host is not available for selection until the host’s data server is ready.

3)     Once the xrootd contacts the cmsd, the host automatically becomes ineligible for selection whenever the data server becomes unready,

4)     The –i option is meant for to be used with data servers that are unable to communicate with the local cmsd. You should not specify this option for the xrootd server.

5)     Warning: the default cmsd mode (i.e., wait for data server) must be used in conjunction with xrootd’s configured for clustering; otherwise the host will never be selected by the manager cmsd.


 

6)      Warning: The –i option disables port remapping. With port remapping, a client is redirected to the port actually being used by the data server that is the target of the redirection. This allows arbitrary or hidden ports to be used, none of which need be the same. When port remapping is disabled, clients are always redirected to the port they initially used to contact the redirector.

7)     The –b option forces the program into the background. If –l is not specified; all output messages are discarded.

8)     The –b, –p, and –s command line options are meant to be used by start-up scripts (e.g. init.d).

9)     Warning: Command line options, except for –s, over-ride corresponding configuration file directives.

 

Example

cmsd –c /opt/xrootd/cmsd.cf


1.3.1       Multiple Instances and Automatic Fencing

 

The cmsd supports running as many cmsd’s as you would like on the same host (i.e., machine). This is accomplished by the n command line option. This option assigns an instance name to the cmsd. The cmsd uses instance name to maintain a separate disk name space for files that it needs to create.

 

There is no default instance name; however, the system uses the word anon to refer to unnamed cmsd’s. By design, there can only be one logical instance combination of a manager, supervisor, and server running on the same machine. The -n option allows you to create new logical instances by assigning each instance a different name. This allows you to run multiple instances of the cmsd on the same machine.

 

Server and supervisor cmsd’s pose no port contention problems since they always use whatever port happens to be free. Manager cmsd’s are assigned specific port numbers (see the manager directive). Therefore, if you wish to run more than one cmsd manager on a host, each manager must also be assigned a unique port number.

 

The cmsd’s always work in pairs with xrootd’s. The pairing only works within the same instance. That is, if a cmsd with an instance name of foo is to be used with a particular xrootd; then that xrootd must be given an instance name of foo as well. Additionally, the cmsd and xrootd home directories should differ to avoid core file conflicts.

 

Failure to follow these directions will prevent proper communications from being established between xrootd’s and cmsd’s.

 

Once an instance name is assigned to a daemon using the –n option, the system automatically fences in the daemon so that it does not interfere with any other xrootd processes running with it. Automatic fencing consists of threse actions:

·       The instance name is suffixed to the adminpath to create a unique location for temporary server files. For instance, if –n is not specified, xrootd creates /tmp/.xrootd/admin as the path for the administrative interface. If “-n test” is specified, xrootd creates /tmp/test/.xrootd/admin instead. Even the path specified with the  adminpath configuration directive is modified.


 

·       The instance name is used to create a new directory in the current working directory. The current working directory is changed to this newly created path. So, if “/home/xrootd” is the current working directory and “-n test” is specified; the current working directory becomes “/home/xrootd/test”. This allows core files to be segregated by instance name.

·       The instance name is automatically inserted into the log file path specified via the –l command line directive to create a unique location for server log files files. For instance, if “–l /var/adm/xrootd/cmslog is specified along with “-n test”, cmsd modifies the –l argument to be  /var/adm/xrootd/test/cmslog.

 

Automatic fencing of log files may, for some installations, run counter to the way log files are commonly handled. You can disable fencing of log files by prefix the log file path by an equals sign. However, you are then responsible to make sure that each instance uses a different log file path or name.

 

1.3.2       Log File Plug-Ins

XRootD allows you to specify a plug-in to handle messages that would otherwise be sent to a regular file or standard error. You do this using the ‘@’ qualifier with the –l option. Logging messages is a critical function in the server and any delay will severely impact server performance. The default logging path is very efficient and any plug-in placed in the path should be just as efficient. To help, a speed matching buffer is used to minimize plug-in vagaries. However, if you choose to not use a speed matching buffer (i.e. a bsz of zero for synchronous operation) then the plug-in becomes the choke point in server performance.

 

You may also choose to capture standard error output using the cse parameter. However, this option will result in an infinite loop if your logging plug-in writes to standard error for any reason. This may be mitigated by specifying cse=1 which only sends standard error output to the plug-in if it starts with a timestamp of the form “yymmdd hh:mm:ss”. All debugging output starts with such a timestamp.

 

The details on how you write a plug-in is detailed in the XrdSysLogPI.hh header file. It is important to realize that if you use the XrdSysLogger object to route a message from your plug-in, an infinite loop will result. Additionally, one log file plug-in is used to all XrdSysLogger instances.


 

1.3.3       Files created by cmsd

 

The following files are created by the cmsd:

 

Default File

Type

Modified by

Purpose

<stderr>

 

-l option and

–n option

Informational and error messages

/tmp/[name/].olb/olbd

TCP Socket

adminpath and –n option

Local xrootd – server cmsd communications

/tmp/[name/].olb/olbd.super

TCP Socket

adminpath and –n option

Local xrootd - supervisor cmsd communications

/tmp/[name/].olbd/olbd.notes

UDP Socket

adminpath and –n option

Local cmsd server event notifications

/tmp/[name/].olbd/olbd.seton

UDP Socket

adminpath and –n option

Local cmsd supervisor event notifications

/tmp/[name/]cmsd.pid

File

pidpath and

–n option

Holds the process id and the local path prefix (i.e., localroot) for a server cmsd.

/tmp/[name/]cmsd.mangr.pid

File

pidpath and

–n option

Holds the process id and the local path prefix (i.e., localroot) for a manager cmsd.

/tmp/[name/]cmsd.superpid

File

pidpath and

–n option

Holds the process id and the local path prefix (i.e., localroot) for a supervisor cmsd.

<cwd>//[name/]core[.pid]

File

–n option

Core file.

/tmp/xrootd.name.env

File

pidpath and

–n option or

–s directory

Holds environmental information (see the xrd/xrootd reference).

 

The adminpath directive specifies the directory where the remaining files are written. The pidpath directive specifies the directory where the pid file is written. The -n option specifies the cmsd instance name. If specified, the instance name is automatically suffixed to the adminpath and pidpath, as shown by “[name/].” A directory is also create in the current working directory for core files and the log file destination is modified by inserting “[name/].” in the destination specified by the –l option. If necessary, the directory is created. Note that the pidpath is over-ridden by the –s option and if specified, the environmental information is also placed in the same directory where the pid file is placed.


1.3.3.1      Environmental Information File

The daemon writes environmental information in the directory specified by the –s command line directive and if not specified, in /tmp. This information can be used to automatically collect all relevant information about a daemon to facilitate automatic problem resolution.

 

The environmental file is named “cmsd.name.env” where name is the instance name and anon if no instance name was specified. The format of the information is shown below. When parsing this information, you should not depend on the order shown below.

 

 

pid=pid&host=host&inst=inst&ver=ver&cfgfn=cfgfn&cwd=cwd&logfn=logfn

 

 

Parameters

cfgfn    The configuration file used.

cwd      The current working directory.

host     The host name.

inst      The instance name.

logfn    The log file being used.

pid       The process id.

ver       The version string.

 


 

1.3.4       Exported Environment Variables

 

The following table shows the environment variable exported by xrootd. These may be used by external programs and plug-ins, as needed. They should never be modified.

 

XRD Variable

Contents

XRDADMINPATH

Is the directory for log files. By default, it is XRDBASE/logs.

XRDCONFIGFN

The effective administrative path used for server management files.

XRDCMSCLUSTERID

The globally unique cluster identification for this host.

XRDDEBUG

Set to one when the –d command line option is specified.

XRDHOST

The current host’s DNS name.

XRDINSTANCE

Is the string of the form “execname  instance@hostname”. Where execname is the executable’s name, instance is the name specified via –n or anon if no instance name was specified, and hostname is the current host’s DNS  name.

XRDLOGDIR

Is the directory where log files are written.

XRDNAME

The name specified via –n or anon if no instance name was specified.

XRDPROG

The executable’s name.

XRDROLE

The effective value specified on the all.role directive.

XRDSITE

The site name specified either via the –s command line option or the all.sitename directive.

 

If the standard oss plug-in is being used, the following additional environment variables are exported.

 

OSS Variable

Contents

XRDN2NLIB

The path and name of the name-to plug-in, if specified via the oss.namelib directive.

XRDRMTROOT

The local root path specified by the oss.remoteroot directive.

XRDLCLROOT

The local root path specified by the oss.localroot directive.


2        Mandatory Configuration Directives

 

This section describes directives that are must be specified to configure the Cluster Management Service.

2.1      manager

 

 

all.manager [ meta | peer | proxy ] [ all | any ]

 

            host[+]{:port[@sname] | port[@sname]}

 

            [ if conds ]

 

 

Function

Specify the manager cmsd location.

 

Parameters

meta   Identifies the cmsd meta-managers that cmsd managers should subscribe to.

 

peer    Identifies the cmsd peer managers that cmsd managers should subscribe to as a peer manager.

 

proxy  Identifies the cmsd managers that xrootd servers with proxy roles (i.e., “proxy” or “proxy server”) should subscribe to.

 

all        Uses a load distribution algorithm to select an appropriate manager. See the section “Choosing all vs. any” for non-peer managers and the section “Peer Manager File Location” for peer managers to determine the best option for your cluster.

 

any     Uses a fail-over algorithm to select an appropriate manager. See the section “Choosing all vs. any” for non-peer managers and the section “Peer Manager File Location” for peer managers to determine the best option for your cluster.

 

host     The DNS name or IP address of the cmsd manager. If host ends with a plus sign (+), then the all hosts addresses associated with host are considered to be available managers.

 

port     The TCP port number or service name at which the manager will accept connections. The port may be specified with an adjacent colon or space separation.

 

sname  Places this manager into a group identified by an arbitrary 1- to 63-character name, typically the site name. By default, the name local is used. The sname is only used to support disjoint cluster configurations, discussed later.

 

conds   The conditions that must exist for this directive to apply. Refer to the description of the if directive on how to specify conds.

 

Defaults

None; see the Notes for requirements. If you do not specify all or any, then any is assumed.

 

Notes

1)     You must specify the “manager” directive for each xrootd given a manager role and for every cmsd given a server or supervisor role.

2)     You must specify the “manager peer” directive for every cmsd given a peer or peer manager role.

3)     You must specify “manager proxy” directive for each xrootd given a proxy or proxy server role.

4)     This is a global directive and must be qualified by the “all” prefix.

5)     All non-peer manager cmsd’s use the manager directive to establish a communications channel with each indicated manager.

6)     You may specify up to 16 different managers.

7)     If the manager host name ends with a plus, then all the IP addresses associated with host are treated as managers and every non-manager cmsd and xrootd subscribes to each one. This allows you to easily construct fault-tolerant configurations using DNS IP address aliases.

8)     The host specifies the machine that is running cmsd in a manager role.

9)     IP addresses may be specified in IPV4 format (i.e. “a.b.c.d”) or in IPV6 format (i.e. “[x:x:x:x:x:x]”).

10) Manager IP addresses are resolved once at start-up time and all specified managers should be registered in the DNS.

 

Example

all.manager beastmanager.slac.stanford.edu 1213


2.1.1       Choosing all vs. any for Normal Managers

When more than one manager is present the all and any options control how a manager is selected. Be aware that this section discusses these options for normal managers (i.e. not peer managers). The all and any options as they apply to peer managers are discussed in the next section.

 

In order to understand the all and any options you should be familiar on how xrootd and cmsd managers provide robustness. In the figure below we have three manager xrootd-cmsd pairs. The xrootd accepts file-oriented requests and asks the cmsd to resolve the files location. The xrootd client provides robustness by simply selecting at random some working xrootd. This distributes the load across all xrootd daemons. On the other hand, each xrootd daemon actually connects to all possible cmsd manager daemons and now has a choice of which working manager to use. The all and any options only affect how an xrootd daemon selects a cmsd.

 

When all is specified, the cmsd uses a hash of the target file name to determine which manager is to handle the file lookup request. This effectively distributes the load across all available managers. If one of the managers fails, it is temporarily replaced by another working manager until the failed manager becomes operational and the load can once again be equally distributed. The manager selection algorithm is effective even when multiple managers fail.  Choose the all option if you expect a heavy file lookup load.

 

When any is specified, the cmsd designates one of the managers for all file lookup requests. If that manager fails, the next available working manager is used. When the failed manager becomes operational it is once again designated as the preferred manager. This option provides simplicity for debugging file location problems since only one manager is handling all file lookup requests and only one log usually needs to be consulted. Use the any option when you expect light loads. Consider using the all option if you see one of the cmsd using more than about 4% of the CPU or grow beyond 1 GB of memory.


 

2.1.2       Peer Manager File Location and Selection

 

The manager directive with the peer option identifies managers of other peered clusters. It is only used by servers that have a non-proxy manager or meta-manager role. Peer clusters are destinations of last resort. When a file cannot be found in the cluster and there is an eligible peer cluster that could potentially serve the file, the client is redirected to the peer cluster. Peer clusters are never searched for a file by another peer manager. In effect, they are independent clusters that may or may not have the file of interest.

 

A peer cluster can have its own set of peer clusters and generally peer relationships are reciprocal in nature. That is if manager A has peer B then B would naturally name A as its peer manager. When a client is redirected to a peer, the redirecting manager prohibits that peer from redirecting back to it. This avoids a redirection loop.

 

Peer selection is controlled by the any and all options. The default is all which means clients will be redirected to peers in the order they are listed. For instance, if two peers are listed as in order B and C then a client will always be redirected to B unless B is not available, in which case it will be redirected to C.

 

When any is specified on the first manager peer directive, then clients are redirected to peers in least recently used order. Unlisted peers subscribing to a manager receive the any option. If all is in effect, these peers are selected last.

 

Because peer clusters are never searched by a peer manager, locate requests directed to a peer manager do not, by default, list peers. In certain contexts, this may produce less than optimal results (e.g. xrdcp extreme copy mode). The kXR_locate kXR_addpeers option may be used to also display eligible peers. It is important to remember that these peers might not have the file in question and a manual search is needed to determine if they do. This automatically happens in recursive location requests but should be avoided for broad requests (e.g. directory listing) in order to minimize network traffic.

 

Displayed peers cannot be readily differentiated from local resources. However, it is possible to restrict locates to peers by prefixing the path with an equals sign (“=”). The result indicates which peers need to be searched determine the file’s actual location.

 

2.1.3       Disjoint Cluster Configurations

Text Box:  
Figure 2.1.3 1: Uniform Cluster

Figure 2.1.3 2: Uniform Cluster

Normally, the manager directive identifies all of the managers for a particular collection of servers, called a cluster. When you identify more than one manager, the members of the cluster assume that the managers are functionally identical (i.e. merely replicas setup for enhanced reliability). The figure o the right shows such a configuration. Here SM, a server, joins the two managers, M-A1 and M-A2, of Cluster A. Then SM becomes part of that uniform cluster. Thus, a request issued by one of the managers is automatically done relative to all of the managers. This provides cluster cohesion regardless of how many managers exist and the all.manager directive is the same for all members of cluster A.

 

For instance, if one of the managers of a cluster blacklists and redirects a member of the cluster, that member assumes that the redirect is to be taken relative to all of the managers. Hence, the member disconnects from all of the managers and connects to the nodes to which the member was redirected by one of the managers.

 

This mode of operation is correct as long as all of the managers are indeed replicas of each other. However, it is possible to construct a cluster whose members provide resources to two disjoint clusters, say A and B, as shown in the figure to the left.  In this case, SM still needs to identify the managers of A and the managers of B. But in this case, they really are not replicas of each other. Indeed, managers of A are distinct from the managers of B. Treating all of them identically would quickly make such a configuration dysfunctional.

 

SM avoids such a conflict by using the sname qualification in the all.manager directive when defining the managers in its own configuration file. Here, managers in cluster A were qualified with @A while managers in cluster B were qualified with @B. This allows SM to treat these as two as unrelated managers yet provide services to both managers in a uniform way.

 

The ‘@’ suffix is an arbitrary name and is merely used to distinguish the managers. If you employ site naming (i.e. xrd.sitename directive) then the suffix should be the site name assigned to each cluster. This makes log file messages more descriptive; especially for such a complex cluster configuration.

 

Had SM been a manager, then the all.manager directive in its configuration file would identify he managers of A and B as meta-managers, as

 

all.manager meta hostname:port@sname

 

Finally, you can avoid listing each individual manager by manager by creating a DNS entry that is associated with two address records, one for each manager in the cluster. Doing this would allow you to simply enter he DNS alias for both managers indicating that he addresses should be automatically expanded as in

 

all.manager meta hostname:port+@sname

 

 


2.2      role

 

 

all.role rolename [ if conds ]

 

rolename: [meta | proxy] manager | [proxy] server |

 

          [proxy] supervisor

 

 

Function

Designate the role the server is to have.

 

Parameters

rolename

The server’s role in the configuration. See the usage notes and the following section for an explanation of roles.

 

conds   The conditions that must exist for this directive to apply. Refer to the description of the if directive on how to specify conds.

 

Defaults

all.role manager

 

Notes

1)     This is a global directive and must be qualified by the “all” prefix.

2)     Do not specify the all.role directive when configuring a stand-alone XRootD server. This directive specifies that the server is part of a cluster and that a local cmsd exists. Stand-alone servers, by definition, do not have a cmsd. Failure to ignore this will fill the log with error messages indicating that the local cmsd cannot be contacted.

3)     A role of manager indicates that the cmsd is at the top-most level of the server hierarchy and is used to locate files.

4)     A role of server indicates that cmsd is at the bottom-most level of the server hierarchy and is used by pure data servers to serve data files.

5)     A role of supervisor indicates that the cmsd is at an intermediate-level of the server hierarchy and is used to bridge the top-most level and the bottom-most level.

6)     A role of meta manager indicates that cmsd is to act as a manager and accept subscriptions from other managers. Meta managers allow you to federate administratively independent clusters.

7)     A role of proxy indicates that the xrootd is at the top- and bottom-most level of the server hierarchy. When contacted, the xrootd acts like a manager to locate the target file. However, unlike a true redirector, the xrootd actually performs the requested operation as if it were a server acting in behalf of the client making the request.

8)     Any xrootd’s designated as proxies may only communicate with cmsd’s that have also been designated as proxies.

9)     The following table describes the effect each role has on an xrootd server and its corresponding cmsd server.

 

Example

all.role supervisor if sup*.slac.stanford.edu

 

2.2.1       Role Summary Table

 

Role

cmsd

xrootd

manager

Provides a search service across one or more “server” or “supervisor” cmsd’s.

Logs into one or more cmsd’s, identified by the “manager” directive, and provides a redirection service

server

Subscribes to a “manager” cmsd, identified by the “manager” directive, in order to form a cluster and accepts logins from a local xrootd.

Logs into a local “server” cmsd and provides data from a locally accessible file system.

supervisor

Same as “server” plus provides a search service across one or more server or supervisor cmsd’s.

Logs into a local “supervisor” cmsd and provides a redirection service.

meta manager

Provides a search service across one or more “manager”  cmsd’s.

Logs into one or more meta manager cmsd’s, identified by the “manager meta” directive, and provides a redirection service

Role

cmsd

xrootd

proxy manager

Same as “manager” but only accepts cmsd’s and xrootd’s that have a “proxy” role (i.e., can only manage proxies).

Same as manager role except that the manager cmsd’s must also have a proxy role.

proxy server

Same as “server” except that managers and the local xrootd must also have a proxy role.

Same as “proxy” and logs into a local “proxy server” cmsd to be part of a cluster.

proxy supervisor

Same as “supervisor” but only allows proxy cmsd subscriptions (i.e., can only manage proxies).

Logs into a local “proxy supervisor” cmsd and provides a redirection service.

 

 


3        Common Configuration Directives

3.1      adminpath

 

 

all.adminpath path [ group ]

 

 

Function

Designate the path used for administrative communications.

 

Parameters

path     is the path to use for Unix named sockets.

 

group

Allows group access to path.

 

Defaults (see warning in the notes)

            The default administrative path is “/tmp/.olb”.

 

Notes

1)     Warning: if idle /tmp directories and socket files are automatically deleted by the system, you should specify a different stable path; otherwise, the system may become unresponsive. Normally, “/var/run/cmsd” is used.

2)     Unless group is specified, only the user running cmsd can write to the named sockets. This is done to ensure that non-privileged users cannot send cmsd administrative requests.

3)     The server, manager, and supervisor cmsd’s create stream sockets named

olbd.admin”, “olbd.nimda”, and “olbd.super” in this directory, respectively. These sockets are used for administrative communications.

4)     The server and manager cmsd’s respectively create datagram socket named “olbd.notes” and “olbd.seton” in this directory. These sockets are used for external notifications.

5)     The adminpath is modified by the –n command line option.

 

Example

            all.adminpath /var/run/cmsd


3.2      allow

 

 

cms.allow { host | netgroup } name

 

 

Function

Restrict the hosts that can subscribe to the manager cmsd.

 

Parameters

host name

The DNS host name or IP address allowed to subscribe to the cmsd. Substitute for name a host name or address. The host name may contain a single asterisk anywhere in the name. This lets you allow a range of hosts should the names follow a regular pattern. IP addresses may be specified in IPV4 format (i.e. “a.b.c.d”) or in IPV6 format (i.e. “[x:x:x:x:x:x]”).

 

netgroup name

The NIS netgroup allowed to subscribe to the cmsd. Substitute for name a valid NIS netgroup. Only hosts that are members of the specified netgroup are allowed to subscribe to the cmsd.

 

Defaults

            None. If allow is not specified, any host is allowed to subscribe.

 

Notes

1)     This directive is only used by manager-mode cmsd’s.

2)     You may specify any number of hosts and netgroups. Any host matching a specified name or is a member of a specified netgroup is allowed to subscribe to the cmsd.

3)     Warning! Using hostname based security relies on the security of the DNS server and the inability of other hosts spoofing and successfully using the “allowed” IP addresses. The two security assumptions have severe limitations.

4)     Use strong authentication to provide a more robust security framework. Refer to the seclib directive for more information.

 

Example

            cms.allow host kandata*.slac.stanford.edu   


3.3      defaults (an oss directive)

 

 

oss.defaults options

 

options: [no]check [no]compchk [no]dread

 

         {forcero | readonly | r/o | r/w | [not]writable}

 

         {inplace | outplace} {local | global | globalro}

 

         {[no]mig | [not]migratable} [no]mkeep [no]mlock

 

         [no]mmap [no]rcreate [no]ssdec [no]stage

 

 

Function

Specify default file processing options.

 

Parameters[4]

Option

Disabled/Enabled Function

Default

forcero

Convert all file open requests to read-only access (cmsd & oss).

writable

local

Do not export this path via the cluster manager (cmsd only).

global

global

Export this path via the cluster manager (cmsd only)

global

globalro

Export this path via the cluster manager as read-only (cmsd only).

global

readonly

r/o

Files may only be opened for read access (cmsd & oss).

writable

r/w

Path is writable (cmsd & oss)

writable

[no]stage

[Do not] stage a file from a remote storage system should it not exist in the local file system at open time.

nostage

[not]writable

Path is [not] writable (cmsd & oss).

writable


Notes

1)     This directive is identical to the oss.defaults directive and establishes the defaults for the export directive. This allows you to keep a single configuration file for cms and oss components.

2)     Directive options may be applied to selected paths using the export directive. This allows you to selectively over-ride the default,

3)     The defaults directive should be specified prior to any export directives.

 

Notes on forcero and readonly

1)     The forcero and readonly options declare any files prefixed by the path to be non-writable. The cmsd excludes all servers declaring the prefix as non-writable when looking for a file that is to be modified or created.

2)     The mlock, mkeep, and mmap options cause a path to have the forcero attribute.

 

Notes on local, global, and globalro

1)     The local option prevents the applicable paths to be seen by the manager cmsd; making them globally inaccessible via the redirector.

2)     The global option makes a path eligible to be used by the manager cmsd and associated redirector. This is the default.

3)     The globalro option makes a path eligible to be used by the manager cmsd and associated redirector in readonly mode; regardless of how it is actually declared for the server. This allows you to export local writable paths as global readonly paths.

 

Notes on [no]stage

1)     When stage is in effect, files are dynamically staged from a remote storage system to local file space when opened, if the file is not already locally on disk. The cmsd selects servers that can stage the file should no other server have the file or if otherwise eligible servers are overloaded or unavailable.

2)     When nostage is in effect, the server claims that the files must exist on disk in order to be accessed.

3)     The nostage and stage directives may be applied to selected paths using the path directive.

 

Example

            oss.defaults stage forcero


3.4      dfs

 

 

cms.dfs [limit [central] [=]rate]

 

        [lookup {central | distrib}] [mdhold mdtm]

 

        [qmax qmax] [redirect {immed | verify}]

 

        [retries rmax]

 

 

Function

Configure distributed file system handling.

 

Parameters

limit   Establish limits on meta-manager requests. The limit is applied in the manager node when central is specified. Otherwise, the limit is applied where file systems look-ups occur (see lookup). The rate specifies the number of look-ups per second allowed. When rate is preceded by an equals sign (=), look-ups are metered to occur exactly at the specified rate. Otherwise, the system uses a median-average algorithm. See the notes on how these algorithms differ. By default, no limit is applied and is equivalent to specifying zero or a value greater than 1000 for rate.

 

lookup

            Specifies where file existence checks are to be performed. By default, they are performed on data server nodes (i.e. distrib). If the manager node has access to the distributed file system, file existence can be checked by the manager if central is specified. See the notes on the pros and cons of using central vs. distrib look-ups.

 

mdhold

            Instructs data servers to keep track of missing directories for mdtm time. The mdtm may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively. When a look-up for a non-existent file occurs, the data server automatically looks-up its parent directory and records whether or not it exists. If the directory does not exist, the fact is remembered for mdtm. Otherwise, the fact that the directory exists is remembered for mdtm*10. Subsequent look-ups for files in missing directories will immediately fail. See the notes on appropriate values. The default is zero which turns this optimization off.

 

qmax  Specifies the maximum number of look-ups that can be queued for processing. When qmax is reached, the oldest unprocessed look-ups are deleted and no look-up is performed; effectively returning a “file does not exist” response. The qmax is ignored if no rate limit applies. The minimum value is 1. The default value is rate*2.5.  See the notes on how this interacts with rate.

 

redirect

            Specifies how the manager is to handle file look-ups by clients. When immed is specified, no look-up is performed and the client is immediately directed to the most suitable data server where the client re-drives the look-up. This is the default for proxy managers. When verify is specified, the manager first determines whether or not the file exists (either locally or via a server query, as specified by lookup) and if the file exists, the client is directed to a suitable server. This is the default for non-proxy managers. See the usage notes on how this option affects performance.

 

retries

            Specifies how many servers a client may exclude when reselecting a server in the DFS cluster due to an error. The default is 2.

 

Defaults

Proxy manager:

cms.dfs limit 0 lookup distrib mdhold 0 redirect immed retries 2

 

Otherwise:

cms.dfs limit 0 lookup distrib mdhold 0 redirect verify retries 2

 

Notes

1)     When you specify the dfs directive, the cmsd optimizes file processing to avoid duplicate requests for the file. A distributed file system is essentially a shared-everything system and if one data server has access to a file, all data servers have access to the same file. Examples of distributed file systems are: dCache, GPFS, HDFS, Lustre; and xrootd proxy servers.

2)     By default, the cmsd assumes a shared-nothing system where each data server has its own independent file system. In order to determine who has a file, all data servers are necessarily interrogated.

3)     As in shared-nothing systems, the cmsd still honors the exported paths declared by servers in a shared-everything system. So, while each server has access to all files in the file system you may logically restrict access by exporting different paths from each server.

4)     The limit parameter only applies to meta-manager requests and provides you with the option of limiting the impact of external queries. If the limit is set too low or is set much higher than the ability of the underlying file system to handle look-ups (i.e., stat()), files will appear to be non-existent to the meta-manager at the queried node.

5)     When limit is specified, the default is to use a median-average algorithm to limit look-ups. This algorithm allows for brief bursts of activity before applying deterministic pacing. This kind of algorithm is much more responsive and requires less CPU time. However, it can subject the underlying file system with up to 50% of the allowed look-ups in a very brief period of time. The alternative is to pace the look-ups at a deterministic rate. While this is not as responsive and requires more CPU time, it guarantees a predictable file system load.

6)     The limit rate is directly affected by the lookup parameter. When look-ups are done by managers (i.e., lookup central) the actual rate is equal to the specified value times the number of managers configured to talk to a meta-manager. When look-ups are done by data servers (i.e., lookup distrib, the default) the actual rate is equal to the specified value times the number of data servers whose manager talks to a meta-manager. In either case, the number of meta-managers does not affect the rate.

7)     In general, it is rare that a limit needs to be specified and is normally not recommended.

8)     The lookup parameter controls where file look-ups occur. The default is to spread look-ups across all of the data servers. This greatly increases scalability at the cost of increased latency. If the look-up request rate is relatively low or the underlying file system can process a look-up in less than a few milliseconds, then specifying central can reduce the latency while maintaining reasonable scalability. The underlying distributed file system must be available to the manager when central look-ups are enabled. The choice of look-up impacts the specified limit, if any.


 

9)     The mdhold parameter allows you to reduce the overhead when looking up missing files when look-ups are done for files in a missing directory. The mdhold parameter control how long the cmsd is to remember that a directory is missing. Future look-ups in a missing directory immediately fail without actually checking the underlying file system during this time. Since the cmsd has no way of knowing if a directory was actually created during this time, the hold time should be set to a small value and should not be specified at all if directories are actively created for files likely to be looked up either by the meta-manager or the manager. Excessively long hold values will likely result in files being incorrectly tagged as missing.

10) The mdhold processing occurs where look-ups are preformed (see the lookup parameter). The limit parameter does not apply to directory look-up requests.

11) The qmax parameter controls the maximum number of outstanding look-up requests. It is only meaningful when a limit is in effect. Look-up queues may occur when the limit is set too low or when the actual file system look-up rate is lower than the specified limit. When the queue limit is reached, the oldest requests are discarded and the file is deemed missing for those look-up requests.

12) The redirect parameter can also be used to optimize look-ups. In immed mode (the default for proxy managers), the manager immediately redirects clients to a suitable data server without any file look-up at all. The server is responsible for doing the look-up. In verify mode (the default for non-proxy managers), the manager performs the look-up to ensure that a selected data server will in fact be able to process the client’s request. The choice of mode should be done in the context of how clients reach a manager node. If most of the activity is local to the cluster then verify mode is usually better. If most of the activity is generated by meta-manager redirects then immed mode is usually better.

13) The retries option provides a limit on how many times a client may reselect a server. The notion is that since all servers in a DFS cluster are the same, an error encountered on one would also occur on any other DFS server. The default allows for two tries before the error is considered permanent. This avoids needlessly redirecting clients to other servers.

 

Example

            cms.dfs lookup central mdhold 1m


3.5      export

 

 

all.export   path [ xoptions ] [ options ]

 

 

Function

Specify processing options for any path matching the specified path prefix.

 

Parameters

path     The path prefix to which the specified options apply. If no options are specified, the current defaults are used.

 

xoptions

xrootd options to apply to any path whose prefix matches path. See the export directive described in the xrd/xrootd configuration reference.

 

options

oss and cmsd-specific (i.e., local, global, and globalro) options to apply to any path whose prefix matches path. Refer to the oss.defaults directive for a detailed explanation of these options.

 

Defaults

All paths are processed according to the default options in effect at the time the path directive is encountered. Defaults are set using the defaults directive.

 

Notes

1)     Any number of export directives may be specified. They are cumulative and are checked in decreasing length order (i.e., most-specific to least specific).

2)     The export directive is usually defined when configuring xrootd and the oss component. Additional cmsd-specific options may also be included.

3)     The export directive is used by xrootd and cmsd to determine which paths are valid for incoming client requests.

4)     The export directive is used by oss component to enforce desired processing attributes.

 

 

Example

            all.export /xrd/files/staged mig nodread rcreate


3.6      localroot (an oss directive)

 

 

oss.localroot path

 

 

Function

Specifies where the local file system name space is actually rooted.

 

Parameters

path     The path to be pre-pended to any local path specified by a client request.

 

Defaults

None. Paths are used locally as specified.

 

Notes

1)     The localroot parameter allows you to keep the external namespace consistent even when you move the associated file system from one location to another. Say that a file system is mounted at /xrd. This means that all file paths start with./xrd. If now you needed to mount the file system at /usr/xrd then by specifying

oss.localroot /usr

the external view of the file system would remain the same since oss will automatically prefix all paths with /usr and use the new mount point.

2)     The cmsd honors the oss localroot directive. This allows you to use a single configuration file for the cms and oss components.

 

Example

            oss.localroot /usr


3.7      perf

 

 

cms.perf parms

 

parms:   [ int time ] [ pgm prog ]

 

 

Function

Specify how load is computed and reported.

 

Parameters

int time

The estimated time between load reports as computed by prog. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

pgm prog

The program that computes the machine load and write the information to standard out. The pgm parameter must be the last parameter on the line.

 

Defaults

cms.perf int 3m

 

Notes

1)     This directive is only used by server-mode cmsd’s.

2)     There is no default value for the program and load information cannot be collected and reported unless a load collector exists. A sample program, cms_MonPerf, is supplied for this purpose. This program uses the rperf command, among others, to calculate the cpu, i/o, and various other load levels.

3)     The specified program is started by the server-mode cmsd at startup time. It is automatically restarted after two failures to report a load within the specified interval.


4)     The specified program must write 5 white-space separated numbers to standard out. The last number must be terminated by a new-line character (“\n”). Each number must be normalized to 100, with 0 indicating no load and 100 indicating saturation. The numbers are in the order:

1.     system load

2.     cpu utilization

3.     memory utilization

4.     paging load, and

5.     network utilization.

 

Example

cms.perf int 5m pgm /usr/etc/ooss/olb_MonPerf 300


3.8      prep

 

 

cms.prep [echo] [reset cnt] [scrub time] [ifpgm ifprog]

 

 

Function

Specify how offline file preparation is done.

 

Parameters

echo    Writes to the log all of the files found in the external in-preparation queue whenever a reset occurs.

 

reset cnt

The maximum number of scrubs of the in-preparation queue that can be done before the contents of the queue are recomputed. The default is three (3).

 

scrub time

The time between scrubs of the in-preparation queue. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively. The default is 20 minutes.

 

ifpgm ifprog

If specified, ifprog replaces the default built-in prepare mechanism and becomes the interface that adds, removes, and lists preparation queue files. The following section describes the input, output, and calling conventions that ifprog must have. The ifpgm parameter must be the last parameter on the line. Any parameters after ifprog are passed to the program via the argument list. Quoted values must be avoided as they are not correctly passed.

 

Defaults

None. Preparation queue handling is normally disabled.

 

Notes

1)     This directive is only used by server- and manager-mode cmsd’s.

2)     The default prepare mechanism relies on the File Residency Manager’s frm_xfragent. You must configure and run frm_xfrd to successfully implement the default prepare mechanism.

3)     Each cmsd that can stage files is also capable of preparing files to be online prior to their active use. This is done through the prepare protocol. The mechanism that is actually used to bring files to local disk is the responsibility of the external infrastructure.

4)     The prep directive enables and, optionally, describes the interface to that infrastructure. If you do not specify the prep directive, even with no arguments, file preparation is disabled.

 

Example

cms.prep scrub 10m ifpgm /opt/xrd/bin/prep_mngr


 

3.8.1       Optional Prepare Interface Program Requirements

 

Most installation chose the default mechanism to route file preparation requests. This employs the File Residency Manager along with frm_afragent and frm_xfrd. Refer to the File Residency Manager Reference for full details. If you have special needs, you can over-ride the built-in default by specifying an ifprog (see previous section). The requirements of this program are:

 

1)     The ifprog is used to add, remove, and list reparation queue files. When specified, it is started at initialization time and is expected to run continuously, and is automatically restarted should it fail. Parameters are sent via standard in, one request for each new line terminated record. Except for the “list” (i.e., ?) request, the program should not write any output to standard out. Output to standard error is included in the cmsd log file.

2)     When the cmsd needs to know the exact contents of the preparation queue (e.g., files waiting to be brought to local disk) it sends a single question. Refer to the default prepare query message for the exact response requirements.

3)     The format of the messages sent to the program is described under the prepmsg directive. To the prepare query message description for the required response.

4)     If prepare notification is requested, the command should adhere to the following message format:

 

Successful:          ready         requestid msg path

Unsuccessful:     unprep      requested msg path

 

requestid     is the request identifier associated with the completed request.

msg             is the text that followed the notification url (see the prepmsg directive). This text must be sent without inspection.

path            is the logical name of the file that successfully prepared or whose preparation failed.

5)     Because file preparation is done on a best-effort philosophy, the preparation program is free to honor (or not) the requests in any way. Currently, the cmsd does not check the return status of the program nor expects any error output (e.g., messages).

 


3.8.1.1      Default Prepare Request Message (prepmsg)

 

The default[5] message that is sent to the prep ifpgm’s stdin when a prepare operation is required has the following format:

 

 

+[traceid] requestid npath prty mode path [path [ . . . ]]

 

 

Where:

traceid       The unauthenticated identifier associated with the client making the request. The traceid is automatically included when communicating with the File Residency Manager (frm).

 

requestid   The request identifier that can be used to group this request into a unique set of requests. The requestid is globally unique.

 

npath         The notification path to be used to indicate how the request complete. This field may contain:

-                                                                    no notification is to be sent.

file:////path                       send msg via local named pipe named path

mailto://user                   send e-mail to user
tcp://rhost:port/msg       send msg via tcp to rhost:port

udp://rhost:port/msg     send msg via udp to rhost:port

 

prty           The request priority: 0, the lowest, to 2, the highest.

 

mode         The processing mode and may contain a combination of the following letters:

                  f    send fail notice (not affected by q flag)

                  n    send success notice

                  q    suppress default failure notice (i.e., quiet)

                  r    file is expected to be only read

                  w   allow the file to be modified

 

path           The absolute logical name of the file to be prepared. If more than one path is specified, each path is separated by a blank.

 

Notes

1)     You can change the format of a prepare request message with the prepmsg directive. However, you cannot use the supplied frm_pstga and mps_prep[6] commands unless you use the default format.

3.8.1.2      The Prepare Cancel Message

 

The following message is sent to the prep ifpgm’s stdin to cancel a stage operation:

 

 

- requestid

 

 

Where:

requestid   The request identifier used in a previous prepare request. All entries with this requestid should be removed.

 

Notes

1)     You cannot change the format of a prepare cancel request message.

3.8.1.3      The Prepare Query Message

 

The following message is sent to the prep ifpgm’s stdin to cancel a stage operation:

 

 

?

 

 

Notes

1)     The ifprog should respond with a list of new-line separated absolute paths associated with queued requests.

2)     You cannot change the format of a prepare query request message.


3.9      sched

 

 

cms.sched parms

 

parms: [ affinity [default] {none|weak|strong|strict} ]

 

       [ cpu pcpu ] [ io pio ] [ mem pmem ] [ pag ppag ]

 

       [ runq prunq ] [ space putl ] [ fuzz fnum ]

 

       [ gsdflt gsdp ] [ gshr gsp ] [ maxload mload ]

         

       [ refreset sec ]

 

 

Function

Specify the parameters for the load balancing scheduling algorithm.

 

Parameters

affinitity [default] {none|weak|strong|strict}

File affinity policy that the redirector should use when selecting a server.

default           the specified affinity is merely a default and a client may select an alternate affinity using the “cms.aff” CGI tag (see the notes for details). Without default the specified affinity is mandatory.

none               files have no affinity and servers should be selected to distribute requests across all servers. This is the default and uses load information if it has been configured.

weak              files have affinity to the longest-lived server however when the location of the file is not known, the client is directed to the first server that declares it has the file. Otherwise, the longest lived server that has the file is always used. Load information is used if it has been configured.

strong            files have affinity to the longest-lived server and when the location of the file is not known, the client is delayed until all locations of the file are known. Only then is the client redirected longest lived server that has the file is always used. Load information is used if it has been configured.

strict               same as strong but load information is never used even when it is available. This guarantees that the longest-lived server is always chosen regardless of its load.

cpu tcpu

The percentage of cpu load to be used to compute the overall load of a server.

 

fuzz fnum

The percentage difference two overall load values must have before they are considered different. A value of 100 suppresses the use of load in any scheduling decisions.

 

gsdflt gsdp

The default share the meta-manager should use in the absence of a manager-specific value.  The default is 100. See the notes for more information.

 

gshr gsp

The maximum percentage of meta-manager requests that should be directed to this manager (i.e. the global share). The default is 100. See the notes for more information.

 

io pio   The percentage of io load to be used to compute the overall load of a server.

 

maxload mload

The maximum overall load a server may have. Servers whose overall load is greater than mload are not scheduled.

 

mem tmem

The percentage of memory load to be used to compute the overall load of a server.

 

pag tpag

The percentage of paging load to be used to compute the overall load of a server.

 

refreset sec

The number of seconds between server reference count resets. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

runq trunq

The percentage of runq load to be used to compute the overall load of a server.

 

space putil

The percentage of space utilization to be used to compute the overall load of a server when selecting a server to stage or create a file.

 

Defaults

cms.sched cpu 0 io 0 mem 0 pag 0 runq 0 space 0 fuzz 20

cms.sched gshr 100 affinity none refreset 3600

 

Notes

1)     This directive is only used by cmsd’s with manager and supervisor roles.

2)     The load-balancing algorithm chooses from all available servers the server whose computed overall load is smallest. When two servers have the same load, as determined by fuzz, the affinity option controls the selection (e.g. affinity none chooses the least selected server).

3)     Other factors apply in selecting a server. For instance, whether or not the server has the requested file on disk, whether the server is allowed to dynamically stage a file, whether the server has sufficient disk space, etc.

4)     The sum of pctcpu, pctoi, pctmem, pctpag, and pctrunq should be equal to 100.

5)     If the sum of pctcpu, pctoi, pctmem, pctpag, and pctrunq  is equal to zero, or if fuzz is 100, severs are selection is determined by the affinity option (e.g. affinity none performs round-robin selection).

6)     Mode scheduling is also forced when performance monitoring is disabled (see the ping usage directive).

7)     Round-robin selection, with or without load information, is accomplished by using an internal reference counter in order to equalize the selection process. Since this counter may drift due to external anomalies encountered during scheduling, it is periodically reset. The refreset parameter controls the minimal reset frequency. However, the counter is only reset if sufficient selection activity occurred.

8)     The gshr option allows you to set the maximum relative share of requests that a meta-manager subscriber wishes to accept from a meta-manager. Since the percentage is relative its effect is determined by the relative shares of other subscribers to the meta-manager. For instance, if all subscribers indicate the same share then this is equivalent to a share of 100 from the perspective of any individual subscriber. Hence, for global shares to be useful requires some amount of co-ordination between participating subscribers.


 

9)     The global share is used by the meta-manager to select a subscriber only when a choice of subscribers exists (i.e., more than one subscriber has a requested file). In such a case, the meta-manager selects a subscriber so as not to exceed any individual subscriber’s relative share of requests.

10) A subscriber’s share may be temporarily reduced if the subscriber is repeatedly selected because it is the only one which has a requested file.

11) The gsdflt option allows you to specify a default share (e.g. 50). This allows you to treat most subscribers the same and only differentiate those that are exceptions by giving them higher or lower shares than the normal default share.

12) The gshr and gsdflt options only apply to interactions with a meta-manager.

13) When the default is specified in the affinity option, then a client can choose a different affinity using the cms.aff CGI tag as follows:

Tag

Corresponding affinity

Tag

Corresponding affinity

cms.aff=n

none

cms.aff=s

strong

cms.aff=w

weak

cms.aff=S

strict

 

Example

cms.sched cpu 50 io 50


3.10    seclib

 

 

cms.seclib path

or

all.seclib path

 

 

Function

Specify the location of the security interface layer.

 

Parameters

path  The absolute path to the shared library that contains an implementation of the Security (sec) interface that cmsd is to use for strong authentication.

 

Defaults

Strong authentication is disabled unless seclib is specified.

 

Notes

1)     The sec interface allows you to provide an arbitrary authentication implementation (e.g., Kerberos, GSI, etc).

2)     A sec implementation requires that compatible interface libraries be used on the server and client sides of the connection.

3)     Refer to XrdSecEntity.hh and XrdSecInterface.hh for guideline on how to write a sec interface.

4)     If you are using a common configuration file for all components (e.g., xrootd and cmsd) with security enabled; consider the following points. 

a.   If the same security library is used for xrootd and cmsd, specify all.seclib to avoid having to specify the seclib directive twice.

b.   If a different set of protocols is being used for xrootd vs. cmsd, bracket the differences with an “if exec” construct. For instance,

if exec cmsd

security directives for cmsd

else

security directives for xrootd

fi

Example

            cms.seclib /opt/xrootd/lib/libXrdSec.so

 


3.11    space

 

 

cms.space [linger num] [recalc sec]

 

          [[min] [min%] min[k|m|g|t] [[hwm%] hwm[k|m|g|t]]]

 

 

Function

Specify how servers are selected for file creation.

 

Parameters

linger num

The number of times a server may be reselected without an intervening server being selected for allocation. The default is zero (0).

 

recalc sec

The number of seconds between free space recalculations. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

min%  The minimum amount of free space, as a percentage of the largest partition, a server must have in order for it to be selected. If the percentage is less than the min byte value, the min value is used.

 

min     The minimum amount of free space a server must have in order for it to be selected. You may suffix the byte quantity by k, m, g, or t to indicate kilobyte, megabytes, gigabytes, or terabytes, respectively.

 

hwm% The minimum amount of free space, as a percentage of the largest partition, a server must have in order for it to be selected after free space has fallen below min. If the percentage is less than the hwm byte value, the hwm value is used.

 

hwm    The minimum amount of free space a server must have in order for it to be selected after free space has fallen below min. You may suffix the byte quantity by k, m, g, or t to indicate kilobyte, megabytes, gigabytes, or terabytes, respectively.

 


 

Defaults

cms.space linger 0 recalc 15 min 2% 10g 5% 11g

 

Notes

1)     This directive is only used by manager-and server mode cmsd’s.

2)     The space values are used during server selection when either a file is opened in create mode or when a file must be dynamically staged.

 

Example

     cms.space min 2g 10g

3.12    space (an oss directive)

 

 

oss.space group { path | ppfx* }

 

 

Function

Specify the location of one or more disk partitions.

 

Parameters

group  The arbitrary name for the disk partition. Specify a 1- to 63-character name. While the name is required, the cmsd does not use it for any purpose.

 

path     The absolute path at which the disk partition is mounted.

 

ppfx*  All directory entries that start with ppfx in the containing directory are to be used as disk partitions.

 

Defaults

None.

 

Notes

1)     This directive is identical to the oss.space and, now deprecated, oss.cache directives. This allows you to keep a single configuration file for cms and oss components.

2)     In order to redirect staging operations and file creations, the manager cmsd must know how much space is available on each server.

3)     If the xrootd server is running a partitioned file system (i.e., files are allocated via symbolic links to one of many possible file system partitions) then specify each file system partition.

4)     The path may end in an asterisk, indicating that all entries in the parent directory that start with the specified prefix are to be used as a file system partition. This is useful when partition mount points have regular names (e.g., /data/space01, /data/space02, etc.).

5)     If the cmsd does not find any space directives, it infers the file systems to be used using the export directive.

Example

            oss.space public /xrootd/space01  


4        Esoteric Configuration Directives

 

This section describes directives that are normally not specified. You may wish to review these directives to be familiar with additional configuration options that are available.

4.1      altds

 

 

cms.altds port [[no]monitor]

 

 

Function

Specify an alternate data server to pair with a cmsd server.

 

Parameters

port     Is the port number used by the alternate data server to service data requests using xroot protocol. The alternate data server must reside on the same node as the cmsd.

 

[no]monitor

            The option specifies whether or not the cmsd server should monitor the availability of the alternate data server. The default is monitor. Specifying nomonitor makes the cmsd assume that the alternate data server is always available.

 

Defaults

None. The cmsd server assumes it is paired with a standard xrootd server.

Notes

1)     The altds directive allows you to pair a cmsd configured for a server role with a non-standard data server using xroot protocol to supply data on the node where the cmsd is running. Client requests for data available on the node are automatically redirected to the alternate data server.

2)     When monitor is in effect, the cmsd considers the alternate data server available as long as it is able to maintain an unauthenticated login session with the alternate data server.

 

Example

            cms.altds xroot 2094

 

4.2      blacklist

 

 

cms.blacklist [check sec] [path]

 

 

Function

Black list one or more nodes.

 

Parameters

sec       is the amount of time between checks whether or not the blacklist file has been changed. When a change is detected, the file is reprocessed and the blacklist updated.  The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively. The default is 10 minutes (i.e. 10m) and may not be less than one minute.

 

path     is the absolute path of the blacklist file. The default is name of the blacklist file is “cms.blacklist” which is assumed to exist in the configuration file directory.

 

Defaults

            cms.blacklist check 10m configdirpath/cms.blacklist

 

Notes

1)     Blacklisting is not applied unless the cms.blacklist directive is specified. You need not specify any options if the defaults are acceptable.

2)     If the configuration file contains a cms.blacklist directive as well as a cms.whitelist directive, the last such directive applies.

3)     Refer to the following major section on how to code a blacklist file.

4)     The cms.blacklist directive only applies to nodes with a manager or meta-manager role.

5)     Blacklisted nodes are prohibited from logging in. When a node’s login fails because it is blacklisted and is not redirected, the login is retried every minute until it succeeds or fails for another reason.

6)     Black-listed may be redirected to another cluster. If this occurs, then no login retries are attempted at the redirecting host.

7)     Redirection is only supported for CMS clients at version 4.2 or above. Clients below this version are effectively blacklisted and not redirected.


 

8)     Nodes that are already logged in and found to be blacklisted and not redirected are disconnected and prohibited from logging in.

9)     Nodes that are already logged in and found to be blacklisted and redirected are asked to disconnect and retry the login; which causes a redirect. If the node does not disconnect within the ping interval, it is forcibly disconnected.

10) To remove all hosts from the blacklist, simply remove the file.

11) If the blacklist file is not present, no controls are applied (i.e. all connections are allowed to login).

12) If the blacklist file is present but contains a syntax error or cannot be read, the current black is not changed.

 

Example

            cms.blacklist /var/run/cms.blacklist

 

 


 

4.3      cidtag

 

 

cms.cidtag tag

 

 

Function

Specify the tag for the internally generated cluster identifier.

 

Parameters

tag       a 1- to 16-character token. The token is added to the cluster identification string.

 

Defaults

None.

Notes

1)     The altds directive allows you to further constrain the cluster identification string for uniqueness. In most instances, the cmsd generates a globally unique cluster identification string. However, depending on the configuration that may not be possible (e.g. two separate clusters using the same meta-manager as their manager). The cittag directive allows you to further differentiate the cluster identification to make sure it is unique across your clusters.

 

Example

            cms.cidtag dpm01


 

4.4      conwait

 

 

cms.conwait sec

 

 

Function

Set the number of second to delay an xrootd client in the absence of a manager cmsd.

 

Parameters

sec       The number of seconds that a client is delayed when there is no connection to a manager cmsd. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

Defaults

cms.conwait 10

 

Notes

1)     When a client attempts to locate a file and no connection exists to a manager cmsd process, xrootd defers the client for conwait seconds. After the time period expires, the client automatically retries the request.

2)     The time period chosen for conwait should be sufficiently long to establish a connection to a cmsd.

 

Example

            cms.conwait 6


4.5      delay

 

 

cms.delay parms

 

parms:  [delnode sec] [discard num] [drop sec]

 

        [full {sec | *}] [hold msec] [lookup sec]

 

        [nostage nscnt][overload {sec | *}] [peer sec]

 

        [qdl sec] [qdn num] [servers num[%]] [service sec]

 

        [startup sec] [suspend sec]

 

 

Function

Manage processing latency.

 

Parameters

delnode sec

The maximum number of seconds that cmsd should wait to delete an in-use node object. If the object is still in use after sec, it abandoned and its memory lost.  The default is 15 minutes.

 

discard num

The maximum number of times a message can be forwarded before it gets discarded.

 

drop sec

The number of seconds a malfunctioning server is allowed to stay in the configuration before it gets dropped. The delay allows time for a server recover before clients are sent to other functioning servers. Clients are delayed during the recovery window.

 


 

full sec

The number of seconds to delay a client when no eligible servers have sufficient space to place a file. By default, delays due to insufficient disk space are not allowed and when the condition occurs, the client is given an ENOSPC error condition. You may decide that this is a recoverable condition and are willing to let clients wait until disk space becomes available. Specifying an asterisk uses a dynamically computed optimal value (see the notes).

 

hold msec

The number of milliseconds to optimistically hold a file query request waiting for a server to reply that the file is available. Should a server reply within this window, the client is immediately redirected to that server, subject to the qdn value.

 

lookup sec

The number of seconds to delay a client when trying to determine which servers have the requested file on disk.

 

nostage nscnt

            Specifies how many staging servers a client may exclude when reselecting a staging server due to an error. The default is 3.

 

overload sec

The number of seconds to delay a client when all available servers are overloaded. Specifying an asterisk uses a dynamically computed optimal value (see the notes).

 

peer sec

The number of seconds to delay a client when resources are not available in the immediate cluster, peers have been specified but no peers are subscribed

 

qdl sec

The number of seconds by which a query must complete (i.e. query deadline) with a positive response; after which the file is deemed to not exist. By default, the qdl is set to be the same as the lookup value.

 


 

qdn num

The minimum number of servers that must have the file in order to redirect the client within the hold period. The default is 1 which causes an immediate redirection when a server indicates it has the requested file (i.e. the fastest responder wins). Values greater than 64 are set to 64.

 

servers num[%]

The minimum number of servers that must be subscribed for load balancing to be effective. The number may be suffixed with a percent sign. When specified this way, the number of available servers must be no less that the specified percentage of the maximum number of servers ever subscribed to the cmsd manager since startup. This option effectively determines the server quorum necessary for the cmsd to redirect clients.

 

service sec

The number of seconds to delay a client when fewer than num servers are subscribed.

 

startup sec

The number of seconds to delay enabling manager service when initially started. This time period allows for servers to subscribe while client requests are delayed. Clients are delayed “service” seconds during this time.

 

suspend sec

The number of seconds to delay a client when a selected server is in suspend state.

 

Defaults

cms.delay delnode 15m discard 7 drop 10m full 0 hold 178 lookup 5 nostage 3

 

cms.delay overload * peer 0 qdl 5 qdn 1 servers 80% service 15 startup 90

 

cms.delay suspend 30

 

Notes

1)     This directive is only used by manager-mode cmsd’s.

2)     All time values may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

3)     When specified, the qdl value should be greater than or equal to the lookup value.

4)     The overload delay is imposed when all eligible servers have a load greater than the one specified maxload on the sched directive.

5)     The full and load options allow you to specify an asterisk to choose the optimal delay value. The optimal value is computed as

ping.ptime * ping.pcnt + 30

      The value is optimal because the load balancer will see no change in external conditions until this amount of time has gone by. See the ping directive for additional details.

6)     Warning: The 80% default for servers works better as more servers join the configuration since more servers can fail before the system enters a holding pattern. For sites with less than 6 servers, you should specify a fixed number.

7)     When the system enters a holding pattern, also known as safe-mode, clients are delayed until the conditions causing the situation are removed. For example, when the number of servers falls below the quorum established by the servers option, safe-mode is entered. The system remains in safe-mode until a quorum is re-established.

8)     The nostage option provides a limit on how many times a client may reselect a staging server. The notion is that since all staging servers are the same, an error encountered on one would also occur on any other staging server. The default allows for three tries before the error is considered permanent. This avoids needlessly redirecting clients to other servers.

 

Example

            cms.delay lookup 3 full *


 

4.5.1       Relationship Between hold & lookup Delay vs. qdl

The right–side graphic illustrates the relationship between the hold and lookup delay and the qdl (i.e. query deadline) value. Initially, a client makes a file-oriented request (e.g. open, stat, etc). If no cached information exists about the file the cmsd sets a query deadline qdl seconds into the future and issues a file existence query to its subscribers.  The deadline establishes the time at which if no positive response is received the file is deemed not to exist. It then places the client request in a special internal state for hold milliseconds with the expectation of getting a positive response which would direct the client to the correct server. If no positive response is received within the hold period, the client is asked to wait lookup seconds and try again. The client retries after the delay. If no response regarding the file has yet been received and the query deadline has not passed the client is once again told to wait lookup seconds and retry. The graphic shows that the deadline passes at some point during the third lookup delay. So, when the client retries the third time, the client is immediately told that the file does not exist.

 

There are several important aspects to understand. First, the qdl value works best if it is an integral multiple of the lookup value. The lookup value should be small enough not to impact overall performance but large enough to minimize retries. The qdl value should be no larger than needed for the particular cluster configuration. The default values work quite well for LAN-based clusters. Some tuning may be required for WAN based clusters, especially if they are federated clusters with no deterministic performance characteristics.

 

The default hold value is also optimized for LAN clusters and works best if positive response times are rather short. Since no more than about 1000 requests can be placed in hold wait, long hold times become ineffective when even a small fraction of file existence requests produce no positive response. Generally, the special hold state does not provide any benefit for WAN based clusters and should left at the default value.


4.6      fxhold

 

 

cms.fxhold noloc ntime[h|m|s] [htime[h|m|s]] | htime[h|m|s]

 

 

Function

Set the time file existence information is to be cached in memory.

 

Parameters

ntime  The number of seconds file non-existence information may be cached and may be no less than 60 seconds. The time may be suffixed by h, m, or s (the default) to indicate hours, minutes, or seconds, respectively. The default is htime.

 

htime   The number of seconds file existence information may be cached. The time may be suffixed by h, m, or s (the default) to indicate hours, minutes, or seconds, respectively.

 

Defaults

cms.fxhold 8h

 

Notes

1)     This directive is only used by manager-mode cmsd’s.

2)     The time limit for non-existence starts after the cache entry has been fully validated. A cache entry is considered partially validated when a file search is in progress or when server transitions are occurring.

3)     A manager cmsd keeps track of where files are at each server-mode site. To prevent information from getting very stale, it is discarded after the time specified by the fxhold directive.

4)     Setting the cache time too low will substantially increase overhead.

 

Example

            cms.fxhold 3h


4.7      fsxeq

 

 

cms.fsxeq { func } xpath

 

func: chmod | mkdir | mkpath | mv | rm | rmdir | trunc

 

 

Function

Designate the program to handle file meta-data operations.

 

Parameters

func     One or more of the indicated functions (i.e., chmod, mkdir, mkpath, mv, rm, rmdir, and trunc) that are to be handled by xpath.

 

 

xpath   The absolute path to an executable file. The file will be invoked whenever the cmsd is asked to execute one of list functions. Parameters specified after xpath are passed to the program via the argument list. Quoted parameters should not be specified as these are not correctly passed.

 

Defaults

            None. The cmsd will either use the native operating system call or the local xrootd server to perform the functions.

 

Notes

1)     This directive is only used by server-mode cmsd’s.

2)     Any number of fsxeq directives may be specified in order to map different programs to different functions.

3)     The fsxeq directive is meant to be used in those situations where additional processing needs to occur when one of the indicated functions is executed (e.g., a file needs to be deleted from online disk as well as a Mass Storage System).

4)     The cmsd is asked to execute functions only if the ofs.forward directive has been specified for the redirecting file server (e.g., xrootd). Refer to the ofs configuration manual for more information.


 

5)     Each function invokes xpath as follows:

 

Function

Command Invocation

chmod

xpath mode  path

mkdir

xpath mode path

mkpath

xpath mode path

mv

xpath oldpath_newpath

rm

xpath path

rmdir

xpath path

trunc

xpath size path

 

6)     The executable function must return a status code of zero upon success. Upon failure, the status code should map to the appropriate <errno.h> code that describes the failure.

 

Example

            cms.fsxeq mv rm /usr/local/bin/fs_cmsd –c /opt/fs/fs.cf


4.8      namelib (an oss directive)

 

 

oss.namelib path [parms]

 

 

Function

Specify the location of the file name mapping layer.

 

Parameters

path  The absolute path to the shared library that contains an implementation of the Name2Name interface that cmsd is to use to make logical file names to physical name for file system specific operations (e.g., open, close, read, write, rename, etc).

 

parms  Optional parameters to be passed to the Name2Name object creation function.

 

Defaults

A built-in minimal implementation driven via the localroot and remoteroot directives is used.

 

Notes

1)     The Name2Name interface is defined in XrdOucName2Name.hh include file. Refer to this file on how to create a custom file name mapping algorithm.

2)     The Name2Name interface is also used by the oss component of xrootd.

3)     The cmsd honors the oss namelib directive. This allows you to use a single configuration file for the cms and oss components.

 

Example

            oss.namelib /opt/xrootd/lib/libN2N.so


4.9      nowait

 

 

cms.nowait

 

 

Function

Specify that the cmsd should not wait for the data server.

 

Defaults

None, you must specify the nowait directive or start the cmsd with –i to not wait for a data server.

 

Notes

1)     The nowait directive provides for a loose coupling between servers running on the same host. The cmsd executes asynchronously from the host’s data server and can subscribe to a manager before the data server is available on the host.

2)     Without nowait, a host is not available for selection until the host’s data server is ready.

3)     Once the xrootd contacts the cmsd, the host automatically becomes ineligible for selection whenever the data server becomes unready,

4)     The nowait option is meant for to be used with data servers that are unable to communicate with the local cmsd. You should not specify this option for the xrootd server.

5)     Warning: the default cmsd mode (i.e., wait for data server) must be used in conjunction with xrootd’s –t option; otherwise the host will never be selected by the manager cmsd.

6)     Warning: The nowait  directive disables port remapping. With port remapping, a client is redirected to the port actually being used by the data server that is the target of the redirection. This allows arbitrary or hidden ports to be used, none of which need be the same. When port remapping is disabled, clients are always redirected to the port they initially used to contact the redirector.

7)     The nowait directive is automatically implied if you start the cmsd with the   –i option.

 

Example

cms.nowait


4.10    osslib (an ofs directive)

 

 

ofs.osslib path [parms]

 

 

Function

Specify the location of the storage system interface layer.

 

Parameters

path     The absolute path to the shared library that contains an implementation of the storage system interface that ofs is to use for storage access for file system specific operations (e.g., open, close, read, write, rename, etc).

 

parms  Optional parameters to be passed to the storage system object creation function.

 

Defaults

A full-featured built-in implementation is enabled for use by the cmsd.

 

Notes

1)     The storage system interface is defined in the XrdOss.hh include file. Refer to this file on how to create a custom storage system implementation.

2)     A cmsd can automatically become a proxy for another manager cmsd if the osslib implements a proxy mechanism. If you decide to run a proxy cmsd then it and its xrootd counterpart should be configured with a role of server.

 

Example

            ofs.osslib /opt/xrootd/lib/libmyOss.so


4.11    pidpath

 

 

all.pidpath path

 

 

Function

Specify the location of the pid file.

 

Parameters

path  The path to be used to create the file where the daemon’s process id and local prefix are stored.

 

Defaults

The process id file is written into /tmp.

 

Notes

1)     The name of the pid file is determined by the cmsd’s role and the –n option.

2)     If the cmsd cannot create the pid file because either one already exists but is not owned by the cmsd, or the directory permissions prohibit the cmsd from creating new file; initialization fails and the cmsd exits.

3)     To create a specific pidpath exception for the cmsd. Use the “cms” prefix instead of “all”.

 

Example

            cms.pidpath /var/run/cmsd


4.12    ping

 

 

cms.ping ptime [ log ucnt ] [ usage pcnt ]

 

 

Function

Control the keep-alive and load reporting frequency.

 

Parameters

ptime   The time between keep-alive requests sent to each server cmsd. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

log ucnt

The number of usage requests that must be made before the reported usage is logged. A value of 0 suppresses any logging of usage information.

 

usage pcnt

The number of pings that must occur before usage is requested from a server cmsd. A value of 0 suppresses usage requests.

 

Defaults

            cms.ping 60 log 10 usage 10

 

Notes

1)     This directive is only used by manager-mode cmsd’s.

2)     Unspecified values in subsequent ping directives default to the last known value.

3)     Smaller ptime values will discover a failing cmsd is a smaller time window at increasing overhead.

4)     Smaller pcnt values will ask for usage information averaged across a smaller time-window.

5)     Usage information will be requested every pcnt*ptime seconds, assuming ptime is in seconds. Select a pcnt/ptime value that averages usage across a reasonable time window for your load (e.g., 5 to 10 minutes).


6)     Usage information for each cmsd server will be logged every ucnt*pcnt*ptime seconds, assuming ptime is in seconds. Choose any value appropriate to your logging needs. For instance, 1 logs usage every time it is requested while 0, the default, does not log usage.

7)     When pcnt or ptime is set to zero, usage based load balancing is disabled. This means that requests are scheduled round-robin.

8)     In the subsequent example, keep-alive pings occur every 30 seconds. Usage is requested every five minutes and never logged.

 

Example

cms.ping 30 log 0 usage 10

 


4.13    prepmsg

 

 

cms.prepmsg msgline

 

msgline: [text] [var] [msgline]

 

var:     $CGI | $LFN | $PFN | $RFN | $NOTIFY | $OFLAG |

 

         $PRTY | $RID | $eVar

 

 

Function

Specify the message to be sent to a piping prep ifpgm when a prepare request is received.

 

Parameters

text      Arbitrary text.

 

var       A variable whose value is determined by the current request setting. The following variables may be specified:

$CGI              all of the opaque information specified after the question mark in the file path

$LFN              logical file name

$PFN              physical file name as modified by localroot or the namelib plug-in

$RFN              remote file name as modified by remoteroot or the namelib plug-in

$NOTIFY       notification string; as follows:

-                                      no notification is to be sent.

file://path                       send an ofs event message via a Unix pipe named path

mailto://user                send e-mail to user
tcp://rhost:port/msg    send msg via tcp to rhost:port

udp://rhost:port/msg send msg via udp to rhost:port

$OFLAG          a character sequence describing the file open processing flags:

          w – O_WRONLY | O_RDWR    r – O_RDONLY

$PRTY            request priority

$RID              request identifier

$eVar            any variable that has been passed along with the file name as opaque information

 

Defaults

+ $RID $NOTIFY $PRTY $OFLAG $LFN

 

Notes

1)     Variables must begin with a $ (dollar sign) and end with a non-alpha-numeric character.

2)     To include a dollar sign into the message, escape it with a back slash (“\”).

3)     A backslash escape is only recognized when followed by a dollar sign.

4)     Important! The prepmsg msgline is not subject to general set variable substitution.

5)     Except for $CGI, the implicit value of a variable that has not been set is the variable name itself, including the dollar sign.

6)     For $CGI, if no opaque information is found, the variable is substituted with the null string.

7)     The default prepmsg slightly differs from the one given above in that $OFLAG contains additional information. See the description of mode under the prepare directive for additional information.

 

Example

            cms.prepmsg prepare $LFN $PFN $RFN

 


4.14    remoteroot (an oss directive)

 

 

oss.remoteroot path

 

 

Function

Specifies where the local file system name space is actually rooted in the remote Mass Storage System.

 

Parameters

path     The path to be pre-pended to any path sent to the Mass Storage System for processing.

 

Defaults

None. Paths are sent to the Mass Storage System as specified.

 

Notes

1)     The remoteroot parameter allows you to place the online file namespace in a different location within the Mass Storage System. Say that the online file system is mounted at /xrd. This means that all file paths start./xrd. If you specified

oss.remoteroot /usr

then the file namespace would be rooted at /usr/xrd within the Mass Storage system because all paths would be prefixed by /usr before being sent to the Mass Storage System for processing.

2)     The cmsd honors the oss remoteroot directive. This allows you to use a single configuration file for the cms and oss components.

 

Example

            oss.remoteroot /usr


4.15    repstats

 

 

cms.repstats [-]soption [ [-]soption ] [ ]

 

soption: all | frq | shr

 

 

Function

Enable additional statistical reporting.

 

Parameters

soption

The additional statistics to be reported when xrd.report specifies protocol summary reporting. One or more options may be specified. The specifications are cumulative and processed left to right. Each option may be optionally prefixed by a minus sign to turn off the setting. Valid options are:

all                 all possible additional information

frq                 information about the fast response queue

shr                 share usage  

 

Defaults

cms.repstats -all.

 

Notes

1)     See the xrd.report directive in the Xrd/Xrootd reference on how to turn on protocol summary reporting.

2)     When protocol summary information is turned on, the cmsd reports basic information that is usually sufficient for monitoring purposes. The repstats directive allows you to request additional information that may be useful for tuning purposes.

3)     The frq information is only available for cmsd’s with a manager or supervisory role.

4)     The shr information is only available for meta-manager cmsd’s.

5)     The Monitoring Reference on more information about the reported statistics.

 

Example

cms.repstats shr

4.16    request

 

 

cms.request  [delay secd] [fwdwait msf] [noresp num]

 

             [prepwait msp] [repwait secr]

 

 

Function

Specify request timing parameters.

 

Parameters

secd     The number of seconds to delay an xrootd client when the cmsd has not responded in secr seconds to a request to locate the file the client wishes to access. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

msf      The number of milliseconds of wait time to impose between forwarded requests (i.e. mv, rmdir, and rm).

 

num    The number of consecutive secr cmsd response timeouts that may be tolerated before xrootd attempts to find another working cmsd manager.

 

msp     The number of milliseconds of wait time to impose between prepare requests.

 

secr      The maximum number of seconds to wait for a cmsd response. The time may be suffixed by s (the default), m , or h to indicate seconds, minutes, and hours, respectively.

 

Defaults

cms.request delay 5 fwdwait 0 noresp 4 prepwait 33 repwait 3

 

Notes

1)     When a client attempts to locate a file a request is sent to the cmsd to locate the best possible copy of the file. Should the cmsd not respond in secr seconds, xrootd defers the client for secd seconds. After the time period expires, the client automatically retries the request.

 

Example

            cms.request delay 3 repwait 1


4.17    subcluster

 

 

all.subcluster [of] host[+]{:port | port]

 

 

Function

Define a subordinate cluster that is actually part of another cluster.

 

Parameters

host     The DNS name or IP address of the cmsd manager of the cluster that is to accept this subordinate cluster. If host ends with a plus sign (+), then the all hosts addresses associated with host are considered to be available managers.

 

Port     The TCP port number or service name at which the manager will accept connections. The port may be specified with an adjacent colon or space separation.

 

Defaults

None; see the Notes for requirements.

 

Notes

1)     The subcluster directive is processed only for simple manager roles (i.e. not qualified in any way); otherwise, it is ignored.

2)     A subordinate cluster may only join managers within the same DNS domain. Cross-domain clusters are not allowed.

3)     The subcluster directive is cumulative in that the specified managers are additive.

4)     Subordinate clusters are useful for independently defining a special cluster and then making it part of a larger cluster. For instance, a special cluster could be one whose servers all have the same type of storage device (e.g. SSD) and need to be managed as a unit.

5)     This directive must be visible in the cmsd and xrootd configuration files.

 

Example

all.subcluster of headmanager.slac.stanford.edu:1213


 

4.18    trace

 

 

cms.trace [-]toption [ [-]toption ] [ ]

 

toption: all | debug | defer | files | forward |

 

         redirect | stage

 

 

Function

Enable tracing.

 

Parameters

toption

The tracing level. One or more options may be specified. The specifications are cumulative and processed left to right. Each option may be optionally prefixed by a minus sign to turn off the setting. Valid options are:

all                 selects all possible trace levels except debug

debug            traces internal functions in cmsd and the xrootd cmsd client

defer            traces imposed wait responses in cmsd

files            traces file location requests and responses

forward       traces forwarded functions in the xrootd cmsd client

redirect     traces request redirection in the xrootd cmsd client

stage            traces binding of locate requests to servers to have promised to stage in files in cmsd.

 

Defaults

cms.trace -all.

 

Notes

1)     The cmsd –d command line option is equivalent to cms.trace all debug.

 

Example

cms.trace debug


4.19    whitelist