Increasing the Size of a JFS Log Device

This document details the supported procedure for increasing the size of a JFS log device in AIX Version 4.x.

Related documentation

The product documentation library is also available:
http://www.rs6000.ibm.com/resource/aix_resource/Pubs/index.html

In general, IBM recommends that JFS log devices be set to 2 MB for every 1 GB of data to be protected. In some cases, filesystem activity is too heavy or too frequent for the log device. When this occurs, the system will log the following errors:

 LABEL: JFS_LOG_WAIT IDENTIFIER: CF71B5B3
 LABEL: JFS_LOG_WRAP IDENTIFIER: 061675CF

NOTE: For more information on these errors, see the technical document "About Filesystem Serviceability Enhancements in AIX V4," available at AIX TechDocs.

Use the following procedure as a guide to increase the size of a JFS log device.

1. Determine which log device to increase. This can be determined by its Device Major/Minor Number in the error log, enter:

   	errpt -a
   

   An example output follows:

   	Device Major/Minor Number
   	000A   0003
   

   The preceding numbers are hexadecimal numbers and must be converted to decimal values. In this example, hexadecimal 000A 0003 equals decimal numbers 10 and 3.

2. Determine which device corresponds with these Device Major/Minor Numbers, enter:

    	ls -al /dev | grep "10, 3"
   

   If the output from the preceding command reveals that the log device that needs to be enlarged is /dev/hd8, (the default JFS log device for rootvg), continue with step 3; otherwise, proceed to the Increasing the size of a user created JFS log device section.

   NOTE: AIX creates the default JFS log device for rootvg on /dev/hd8 at 1 physical partition (PP). IBM recommends that JFS log devices be set to 2 MB for every 1 GB of data to be protected.

3. Increase the size of /dev/hd8 using the extendlv command as follows:

   	extendlv hd8 1
   

4. Boot the machine into Service Mode (also known as Maintenance Mode).
   1. Select 3: Start Maintenance Mode for System Recovery
   2. Select 1: Access a Root Volume Group
   3. Select 0: Continue
   4. Select the desired rootvg.
   5. Select 2: Access this Volume Group and start a shell before mounting filesystems

   NOTE: For a detailed description on booting in Service Mode, see the technical document "Booting in Service Mode," available at AIX TechDocs.

5. Format /dev/hd8 to use all of the space in the logical volume and answer y, to destroy the log, after entering the following command:

    	logform /dev/hd8
   

6. To exit from the shell, enter:

    	exit
   

   The primary filesystems will automatically mount.

7. Shutdown and reboot with the system key in Normal Mode, enter:

   	sync; sync; sync; reboot
   

Increasing the size of a user created JFS log device

1. Extend the logical volume where the JFS log device resides on with 1 physical partition, enter:

    	extendlv <loglvxx> 1
   

   loglvxx is the name of the JFS log device.

2. Determine which of the mounted filesystems use this log device, enter:

    	mount
   

   The log device is indicated in the last column under options.

3. Unmount these filesystems that use the JFS log device specified in step 2, enter:

    	unmount /dev/<lvname>
   

4. Format the JFS log device to use all of the space in the logical volume and answer y, to destroy the log, after entering the following command:

   	logform /dev/<loglvxx>
   

   loglvxx is the name of the JFS log device.

5. Mount all filesystems you unmounted in step 3, enter:

    	mount <lvname>