Creating file systems on Linux

Before installing IBM® MQ, you might need to create file systems for both the product code and working data to be stored. There are minimum storage requirements for these file systems. The default installation directory for the product code can be changed at installation time, but the working data location cannot be changed.

Determining the size of a server installations file system

To determine the size of the /var/mqm file system for a server installation, consider:
  • The maximum number of messages in the system at one time.
  • Contingency for message buildups, if there is a system problem.
  • The average size of the message data, plus 500 bytes for the message header.
  • The number of queues.
  • The size of log files and error messages.
  • The amount of trace that is written to the /var/mqm/trace directory.
Storage requirements for IBM MQ also depend on which components you install, and how much working space you need. For more details, see Disk space requirements.

Creating a file system for the working data

Before you install IBM MQ, create and mount a file system called /var/mqm which is owned by the user mqm in the group mqm ; see Setting up the user and group on Linux. This file system is used by all installations of IBM MQ on a system. If possible, use a partition strategy with a separate volume for the IBM MQ data. This means that other system activity is not affected if a large amount of IBM MQ work builds up. Configure the directory permissions to permit the mqm user to have full control, for example, file mode 755. These permissions will then be updated during the IBM MQ installation to match the permissions required by the queue manager.

Creating separate file systems for errors and logs

You can also create separate file systems for your log data ( /var/mqm/log ) and error files ( /var/mqm/errors ). If possible, place these directories on different physical disks from the queue manager data ( /var/mqm/qmgrs ) and from each other.

If you create separate file systems the /var/mqm/errors directory can be NFS mounted. However, if you choose to NFS-mount /var/mqm/errors, the error logs might be lost if the network fails.

You can protect the stability of your queue manager by having separate file systems for:
  • /var/mqm/errors
  • /var/mqm/trace
  • /var/mqm/qmgrs
  • /var/mqm/log
In the case of /var/mqm/errors, it is rare that this directory receives large quantities of data. But it is sometimes seen, particularly if there is a severe system problem leading to IBM MQ writing a lot of diagnostic information in to .FDC files. In the case of /var/mqm/trace, files are only written here when you use strmqtrc to start tracing IBM MQ.
You can obtain better performance of normal IBM MQ operations (for example, syncpoints, MQPUT, MQGET of persistent messages) by placing the following on separate disks:
  • /var/mqm/qmgrs
  • /var/mqm/log

In the rare event that you need to trace an IBM MQ system for problem determination, you can reduce performance impact by placing the /var/mqm/trace file system on a separate disk.

If you are creating separate file systems, allow a minimum of 30 MB of storage for /var/mqm, 100 MB of storage for /var/mqm/log, and 10 MB of storage for /var/mqm/errors. The 100 MB minimum allowance of storage for /var/mqm/log is the absolute minimum required for a single queue manager and is not a recommended value. The size of a file system must be scaled according to the number of queue managers that you intend to use, the number of pages per log file, and the number of log files per queue manager.

For more information about file systems, see File system support.

The size of the log file depends on the log settings that you use. The minimum sizes are for circular logging using the default settings. For more information about log sizes, see Calculating the size of the log.

For a client installation, the file system can be mounted on a remote network device, for example NFS.
If you are performing both a client and a server installation, the requirements of the server installation take precedence over the requirements of the client installation.
Allow 15 MB as a minimum for an IBM MQ client.
A new sample IBM MQ MQI client configuration file is created in the var/mqm directory, by the client package, during installation, but only if this file does not exist. This file contains the ClientExitPath stanza. An example mqclient.ini file is shown in Configuring a client using a configuration file.
If you are using a common configuration file for multiple clients, either in the IBM MQ installation directory or in another location using the MQCLNTCF environment variable, you must grant read access to all user identifiers under which the IBM MQ client applications run. If, for any reason, the file cannot be read the failure is traced, and the search logic continues as if the file had not existed.