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How to calculate the total amount of disk space for the recovery logs for one queue manager

Troubleshooting


Problem

You are planning for the file system requirements for one WebSphere MQ (WMQ) queue manager, and you want to understand how to calculate the total amount of disk space for the recovery logs needed for the queue manager

Resolving The Problem

1) The recovery logs for an MQ queue manager are stored in:

/var/mqm/logs/QMgrName

Where QMgrName is the name of the queue manager

You may want to have a specific file system for /var/mqm/logs, separate from the rest of /var/mqm (error logs and actual data for the queues and queue manager).

2) LogPrimaryFiles, LogSecondaryFiles and LogFilePages logging parameters in the qm.ini file determine the number of MQ log files to be created and size of each log file.

The following example shows the default values.

File: /var/mqm/qmgrs/QmgrName/qm.ini
Stanza:
     Log:
         LogPrimaryFiles=3
         LogSecondaryFiles=2
         LogFilePages=4096
         LogType=CIRCULAR
         LogBufferPages=0
         LogPath=/var/mqm/log/QmgrName/
         LogWriteIntegrity=TripleWrite


3) This is the formula for finding the total amount of disk space if all the recovery log files are used:

(LogFilePages x 4 KiloBytes) x (LogPrimaryFiles + LogSecondaryFiles)


4) The following table provides a rounded up estimate of the sizes of each log file based on the number of LogFilePages:

LogFilePages    x 4 KB  =  Size of 1 log file  
 1024 (1K)      x 4 KB  =     4 MB  
 4096 (4K)      x 4 KB  =    16 MB
65535 (64KB)    x 4 KB  =   256 MB  

5) The following table shows the total disk space if all the log files are used, given the default values for LogPrimaryFiles=3 and LogSecondaryFiles=2 when various values for LogFilePages are specified:

LogFilePages ->  Size 1 log file  x (LogPrimaryFiles + = Total disk space
                                    LogSecondaryFiles)   for log files  
  1024       ->       4 MB        x       5            =     20 MB  
  4096       ->      16 MB        x       5            =     80 MB  
 65535       ->     256 MB        x       5            =  1,280 MB (1.3 GB)  
6) The following shows the total disk space if 200 primary + 80 secondary number of logs is used with the maximum value for LogFilePages (64K):

LogFilePages ->  Size 1 log file  x (LogPrimaryFiles + = Total disk space
                                    LogSecondaryFiles)   for log files  
 65535       ->     256 MB        x      280           = 71,680 MB (70 GB)

7) The following shows the total disk space if the maximum of 511 primary + secondary number of logs is used with the maximum value for LogFilePages (64K):

LogFilePages ->  Size 1 log file  x (LogPrimaryFiles + = Total disk space
                                    LogSecondaryFiles)   for log files  
 65535       ->     256 MB        x      511           = 130,816 MB (131 GB)

+++ Further information on disk space requirements

WebSphere MQ 8.0.0 > IBM MQ > Configuring>Availability, recovery and restart > Making sure messages are not lost (logging) > Calculating the size of the log

    About Table 1:
    ... when a persistent message is put to a queue, all the message data must be written to the log to make it possible to recover the message. The size of the log depends, typically, on the number and size of the persistent messages the queue manager needs to handle.
    ...
    Put persistent message:
    750 bytes + message length
    If the message is large, it is divided into segments of 15700 bytes, each segment adding an extra 300 bytes.

WebSphere MQ 8.0.0 > IBM MQ > Planning > Planning your storage and performance requirements > Disk space requirements

WebSphere MQ 8.0.0 > IBM MQ > Installing > Planning your installation > Preparing your system > Creating file systems on UNIX and Linux systems

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Document Information

Modified date:
15 June 2018

UID

swg21667211