Migrating volumes between pools using the CLI

You can migrate volumes between pools using the command-line interface (CLI).

You can determine the usage of particular MDisks by gathering input/output (I/O) statistics about nodes, MDisks, and volumes. After you collect this data, you can analyze it to determine which volumes or MDisks are hot. You can then migrate volumes from one storage pool to another.

Complete the following step to gather statistics about MDisks and volumes:

Use secure copy (scp command) to retrieve the dump files for analyzing. For example, issue the following command:
```
scp clusterip:/dumps/iostats/v_*
```
This command copies all the volume statistics files to the AIX host in the current directory.
Analyze the memory dumps to determine which volumes are hot. It might be helpful to also determine which MDisks are being used heavily as you can spread the data that they contain more evenly across all the MDisks in the storage pool by migrating the extents.

After you analyze the I/O statistics data, you can determine which volumes are hot. You also need to determine the storage pool that you want to move this volume to. Either create a new storage pool or determine an existing group that is not yet overly used. Check the I/O statistics files that you generated and then ensure that the MDisks or volumes in the target storage pool are used less than the MDisks or volumes in the source storage pool.

You can use data migration or volume mirroring to migrate data between storage pools. Data migration uses the command migratevdisk. Volume mirroring uses the commands addvdiskcopy and rmvdiskcopy.

Migrating data using migratevdisk

You can use the migratevdisk command to migrate data between two storage pools. When you issue the migratevdisk command, a check is made to ensure that the destination of the migration has enough free extents to satisfy the command. If it does, the command proceeds. The command takes some time to complete.

Notes:

You cannot use the data migration function to move a volume between storage pools that have different extent sizes.
Migration commands fail if the target or source volume is offline, there is no quorum disk defined, or the defined quorum disks are unavailable. Correct the offline or quorum disk condition and reissue the command.
The system supports migrating volumes between child pools within the same parent pool or migrating a volume in a child pool to its parent pool. Migration of volumes fails if source and target child pools have different parent pools. However, you can use addvdiskcopy and rmvdiskcopy commands to migrate volumes between child pools in different parent pools.

When you use data migration, it is possible for the free destination extents to be consumed by another process; for example, if a new volume is created in the destination parent pool or if more migration commands are started. In this scenario, after all the destination extents are allocated, the migration commands suspend and an error is logged (error ID 020005). To recover from this situation, use either of the following methods:

Add more MDisks to the target parent pool, which provides more extents in the group and allows the migrations to be restarted. You must mark the error as fixed before you reattempt the migration.
Migrate one or more volumes that are already created from the parent pool to another group. This action frees up extents in the group and allows the original migrations to be restarted.

Complete the following steps to use the migratevdisk command to migrate volumes between storage pools:

After you determine the volume that you want to migrate and the new storage pool that you want to migrate it to, issue the following CLI command:
```
migratevdisk -vdisk vdisk_name
```
```
 -mdiskgrp
 mdisk_group_name -threads 4
```
You can check the progress of the migration by issuing the following CLI command:
```
lsmigrate
```

Migrating data using volume mirroring

When you use data migration, the volume goes offline if either pool fails. Volume mirroring can be used to minimize the impact to the volume because the volume goes offline only if the source pool fails. You can migrate volumes between child pools or from a child pool to a parent pool using the addvdiskcopy and rmvdiskcopy commands instead of using the migratevdisk command.Complete the following steps to use volume mirroring to migrate volumes between pools:

After you determine the volume that you want to migrate and the new pool that you want to migrate it to, enter the following command:
```
addvdiskcopy -mdiskgrp mdisk_group_namevdisk_name -autodelete yes
```
where mdisk_group_name is the name of the new storage pool and vdisk_name is the name of the volume that is being copied. Specify yes for the -autodelete to automatically delete the original copy of the volume after the copies are synchronized.
The copy ID of the new copy is returned. The copies now synchronize such that the data is stored in both storage pools. You can check the progress of the synchronization by issuing the following command:
```
lsvdisksyncprogress 
```