Thursday, October 21, 2010

Moving file systems from one volume group to another

Moving file systems from one volume group to another

ATTENTION: Make sure a full backup exists of any data you intend to migrate before using these procedures.

In AIX, storage allocation is performed at the volume group level. Storage cannot span volume groups. If space within a volume group becomes constrained, then space that is available in other volume groups cannot be used to resolve storage issues.

The solution to this problem is to add more physical volumes to the relevant volume group. This may not be an option in all environments. If other volume groups contain the required free space, the alternative is to move the required logical volumes to the desired volume group and expand them as needed.

The source logical volume can be moved to another volume group with the cplv command. The following steps achieve this.

ATTENTION: The logical volume should be inactive during these steps to prevent incomplete or inconsistent data. If the logical volume contains a mounted file system, then that file system should be unmounted first. If this logical volume is being used as a RAW storage device, then the application using this logical volume should close the device or be shut down.

1.Copy the source logical volume to the desired volume group with the cplv command.

For example, where myvg is the new volume group and mylv is the name of the user's logical volume, enter:

cplv -v myvg mylv

This will return the name of the new logical volume, such as lv00.

If this logical volume was being used for RAW storage, skip to to step 6. If this is a JFS or JFS2 file system, proceed to step 2. Note that RAW storage devices should NOT use the first 512 bytes of the RAW device. This is reserved for the LVCB or logical volume control block. cplv will not copy the first 512 bytes of the RAW logical volume, but it will update fields in the new logical volume's LVCB.

2.All JFS and JFS2 file systems require a log device. This will be a logical volume with a type of jfslog or jfs2log for JFS2 file systems. Run the lsvg -l command on your destination volume group. If a JFS or JFS2 log DOES NOT already exist on the new volume group, create one by using the mklv and logform commands as detailed below. If a JFS or JFS2 log DOES exist, proceed to
step 3

With a JFS2 filesystem, you also have the option of using an inline log. With inline logs, the jfs2log exists on the filesyster itself. After the cplv command is ran on a JFS2 inline log filesystem, run:

logform /dev/lvname

You should receive a message about formatting the inline log. If you do not receive a message about an inline log, then this filesystem is not a JFS2 inline log filesystem and you should treat it as a regular JFS2 filesystem. After hitting y on formatting the inline log, continue to step 3.

To make a new JFS log, enter the following command, where myvg is the name of the new volume group, enter:

mklv -t jfslog myvg 1

To make a new JFS2 log, enter: mklv -t jfs2log myvg 1

This will return a new logical volume of either type jfslog or jfs2log, such as loglv00. This new logical volume will need to be formatted with the logform command in order to function properly as either a JFS or JFS2 log. For example:

logform /dev/loglv00

Answer yes to destroy.

3.Change the filesystem to reference a log device that exists in the new volume group and the new logical volume with the chfs command.

For example, where myfilesystem is the name of the user's filesystem, enter:

chfs -a dev=/dev/lv00 -a log=/dev/loglv00 /myfilesystem

With inline logs on JFS2 filesystems this command is also different:

chfs -a dev=/dev/lv00 -a log=INLINE /myfilesystem

4.Run fsck to ensure filesystem integrity. Enter:

fsck -p /dev/lv00

NOTE: It is common to receive errors after running fsck -p /dev/lvname prior to mounting the filesystem. These errors are due to a known bug that development is currently aware of and which will be resolved in a future release of AIX. Once the filesystem is mounted, a future fsck with the filesystem unmounted should no longer produce an error.

Mount the file system.

For example,
where myfilesystem is the name of the user's file system, enter:

mount /myfilesystem

At this point, the migration is complete, and any applications or users can now access the data in this filesystem. To change the logical volume name, proceed to the following step.

NOTE: If you receive errors from the preceding step, do not continue. Contact you AIX support center.

6.Remove the source logical volume with the rmlv command.

For example,

where mylv is the name of the user's logical volume, enter:

rmlv mylv

Rename and reset any needed attributes on the new logical volume with the chlv or chmod commands. In order to rename the logical volume, the filesystem or raw logical volume must be in a closed state.

For example, where mylv is the new name you wish to change lv00 to be, enter:

chlv -n mylv lv00

Logical volumes specific to rootvg

The following logical volumes and file systems are specific to the rootvg volume group and cannot be moved to other volume groups

Logical Volume File System or Description ------------------------------------------------------
hd2 /usr
hd3 /tmp
hd4 /
hd9var /var


Vinod said...

Great work for writing about AIX,
Am a fan of AIX too.. new to AIX.. currently working on it.. You seems to be an expert in the area.. I too have created a blog for AIx, please have look at it and enhance me if I go wrong..

amina said...

thank you for posting this blog it has helped me alot i'm new to AIX can you please post a new blog for AIX sever build life cycle and what could be the problem with an LPAR if it is not functioning properly and how do i diagnose it and how to fix the issue.

khan said...

Hi Santosh ,

My QUESTION IS How to Connect HMC through to Telnet, and SHH ?