System Management Guide: Operating System and Devices - Reduce the Size of a File System in Your Root Volume Group

Reduce the Size of a File System in Your Root Volume Group

The simplest way to reduce all file systems to their minimum size is to set the SHRINK option to yes when restoring the base operating system from backup. The SHRINK option and the following scenario cannot be used in tandem. If you set the SHRINK option to yes after doing the following procedure, the installation overrides your changes to the /image.data file.

This scenario leads you through a manual process to reduce the size of a selected rootvg file system. You will identify a file system that is not using all of its allocated disk space and then reallocate based on the amount of space the file system actually uses, thus freeing more space for the root volume group's use. As part of this procedure, you will back up your volume groups and reinstall the operating system, using the revised allocations.

Attention: This procedure requires shutting down and reinstalling the base operating system. Whenever you reinstall any operating system, schedule your downtime when it least impacts your workload to protect yourself from a possible loss of data or functionality. Before reinstalling the operating system, ensure you have reliable backups of your data and any customized applications or volume groups.

Create a separate backup of all file systems that are not contained in the rootvg. The separate backup helps ensure the integrity of all your file systems.

With root authority, check which file systems in your root volume group are not using their allocated disk space by typing the following command:

df -k

The -k flag displays the file-system sizes in kilobytes. Your result will look similar to the following:

Filesystem    1024-blocks      Free %Used    Iused %Iused Mounted on            
/dev/hd4           196608      4976   98%     1944     2% /                     
/dev/hd2          1769472    623988   65%    36984     9% /usr                  
/dev/hd9var        163840     65116   61%      676     2% /var                  
/dev/hd3            65536     63024    4%      115     1% /tmp                  
/dev/hd1            49152      8536   83%      832     7% /home                 
/proc                   -         -    -         -     -  /proc                 
/dev/hd10opt        32768     26340   20%      293     4% /opt

Looking at these results, you notice a large number of free blocks and a fairly low percentage of use associated with the file system that is mounted on /usr. You decide you can release a significant number of blocks by reducing the number of partitions allocated to the /usr file system.

Check the contents of the /etc/filesystems file to ensure that all file systems in the rootvg are mounted. If not, they will not be included in the reinstalled system.

Create an /image.data file, which lists all the active file systems in the rootvg that are included in the installation procedure, by typing the following command:

mkszfile

Open the /image.data file in your favorite editor.

Search for the usr text string to locate the lv_data stanza that pertains to the /usr file system. Use numbers from this stanza as a base to determine how much you can reduce the /usr file system's number of logical partitions. The default size of each additional logical partition is defined in the PP_SIZE entry of the /image.data file. Your /image.data file would look similar to the following:

lv_data:
	VOLUME_GROUP= rootvg
	LV_SOURCE_DISK_LIST= hdisk0 
	LV_IDENTIFIER= 00042345d300bf15.5
	LOGICAL_VOLUME= hd2
	VG_STAT= active/complete
	TYPE= jfs
	MAX_LPS= 32512
	COPIES= 1
	LPs= 108
	STALE_PPs= 0
	INTER_POLICY= minimum
	INTRA_POLICY= center
	MOUNT_POINT= /usr
	MIRROR_WRITE_CONSISTENCY= on/ACTIVE
	LV_SEPARATE_PV= yes
	PERMISSION= read/write
	LV_STATE= opened/syncd
	WRITE_VERIFY= off
	PP_SIZE= 16
	SCHED_POLICY= parallel
	PP= 108
	BB_POLICY= relocatable
	RELOCATABLE= yes
	UPPER_BOUND= 32
	LABEL= /usr
	MAPFILE=
	LV_MIN_LPS= 70
	STRIPE_WIDTH= 
	STRIPE_SIZE=

The number of logical partitions devoted to this logical volume is 108 (LPs=108).

Determine the number of logical partitions needed by the existing data in the /usr file system by using your result from step 2. You can display the existing file sizes specifically for the /usr file system by using the following command:

df -k /usr

The result repeats the numbers (in kilobytes) you received for the /usr file system in step 2. For example:

Filesystem    1024-blocks      Free %Used    Iused %Iused Mounted on            
/dev/hd2          1769472    623988   65%    36984     9% /usr

Subtract the amount of free space from the total number of 1024-blocks allocated:
```
1769472 - 623988 = 1145484
```
Add an estimate of the space you might need to accommodate any future growth expected in this file system. For this example, add 200000 to the result.
```
1145484 + 200000 = 1345484
```
Divide the result by the logical-partition size in bytes (16*1024) to determine the minimum number of logical partitions you need.
```
1345484 / 16384 = 82.121826171875
```
Use this result, rounded upward, to redefine the number of logical partitions needed (LPs=83).

In your image.data file, change the LPs field from 108 to 83.

Find the fs_data stanza that pertains to the /usr file system. Your fs_data stanza will look similar to the following:

fs_data:
	FS_NAME= /usr
	FS_SIZE= 3538944
	FS_MIN_SIZE= 2290968
	FS_LV= /dev/hd2
	FS_FS= 4096
	FS_NBPI= 4096
	FS_COMPRESS= no
	FS_BF= false
	FS_AGSIZE= 8

Calculate the file-system size (FS_SIZE) by multiplying the physical partition size (PP_SIZE) by 2 (the number of 512-byte blocks used by the physical partitions) by the number of logical partitions (LPs). Given the values used in this example, the calculation is:

PP_SIZE * 512 blocks * LPs = FS_SIZE
16384 * 2 * 83 = 2719744

In your image.data file, change the FS_SIZE field from 3538944 to 2719744.

Calculate the minimum file-system size (FS_MIN_SIZE) based on the actual size of the current data used by the /usr file system, as follows:

Calculate the minimum number of partitions needed. Given the values used in this example, the calculation is:
size_in_use (see step 7a) / PP_SIZE = partitions
1145484 / 16384 = 69.914794921875
Calculate the minimum size required by that number of partitions. Rounding the previous calculation results upward to 70, the calculation is:
```
PP_SIZE * 512 blocks * partitions = FS_MIN_SIZE
16384 * 2 * 70 = 2293760
```

In your image.data file, change the FS_MIN_SIZE field from 2290968 to 2293760.

Save your edits and exit the editor.

Unmount all file systems that are not in the rootvg volume group.

If you have any user-defined volume groups, type the following commands to vary off and export them:

varyoffvg VGName
exportvg VGName

With a tape in the tape drive, type the following command to initiate a complete system backup:

mksysb /dev/rmt0

This type of backup includes the file-system size information you specified in the /image.data file, which will be used later to reinstall your system with the new file-system sizes.

Note

To initiate this backup, you must run the mksysb command from the command line. If you use a system management tool, such as SMIT, the backup creates a new image.data file, overwriting the changes you have made.

Use this backup to reinstall the operating system using the Install With Current System Settings option. During the installation, check that the following options are set appropriately:

Use Maps must be set to no
Shrink the File Systems must be set to no

If you need more information about the installation procedure, see the AIX 5L Version 5.2 Installation Guide.

After the operating system is installed, reboot the system in Normal mode. At this point, the /usr file system is resized, but your user-defined file systems are not available.

Mount all file systems by typing the following command:

mount all

If you receive Device Busy messages about file systems that are already mounted, you can ignore these messages.

At this point, your /usr file system is resized, your root volume group has more free space, and your file systems are usable.