About this task
The migration process can help to ensure that there is
sufficient free space in the storage pools at the top of the hierarchy,
where faster devices can provide the most benefit to clients. For
example, the server can migrate data that is stored in a random-access
disk storage pool to a slower, but less expensive sequential-access
storage pool.
You can control the following options:
- When migration begins and ends
- Migration thresholds are used to control when migration begins
and ends. Thresholds are set as levels of the space that is used in
a storage pool. It is expressed as a percentage of the total space
available in the storage pool. For random-access and sequential-access
disk storage pools, the server compares the threshold to the amount
of data that is stored in the pool as a percentage of the total data
capacity of the volumes in the pool. Total data capacity for sequential-access
disk storage pools includes the capacity of all scratch volumes that
are specified for the pool. For tape storage pools, the server compares
the threshold to the number of volumes that contain data as a percentage
of the total number of volumes available to the pool, including scratch volumes.
You
can also schedule migration activities to occur at optimal times in
your environment. In addition, you can specify the following options:
- How long migration can run before it is automatically canceled
- Whether the server attempts reclamation before migration
- Whether the migration process runs in the background or foreground
- How the server chooses files to migrate
- By default, the server does not consider how long a file has been stored
in a storage pool, or how long since the file was accessed before
it chooses files to migrate. There are optional parameters available
for you to change the default behavior of migration. To ensure that
files remain in a storage pool for a minimum number of days before
the server migrates them to another pool, you can set a migration
delay period for the storage pool. For random-access disk storage
pools, the last time the file was accessed is also considered for
migration delay. For sequential-access storage pools, including sequential-access
disk storage pools that are associated with a FILE device class, all
files on a volume must exceed migration delay period before the server
can migrate all of the files on the volume.
- The number of concurrent migration processes
- You can specify a single migration process or multiple concurrent
migration processes for a random-access or sequential-access storage
pool. You can use multiple concurrent processes to make better use
of your available tape drives, and FILE volumes. Since you can run
migration concurrently on different storage pools during auto-migration,
you must carefully consider the resources (for example, drives) you
have available for the operation.
If simultaneous-write operations
during migration are enabled during multiple concurrent-migration
processing, each process has the following requirements:
- A mount point
- A volume for each copy storage pool, and active-data pool that
is defined to the target storage pool, and the primary pool
Migration processing can differ for disk storage
pools versus sequential-access storage pools. If you plan to modify
the default migration settings for storage pools or want to understand
how migration works, read the following topics:
Remember: - Data cannot be migrated in to or out of storage pools that are
defined with a CENTERA device class.
- If you receive an error message during the migration process,
refer to IBM Tivoli Storage Manager Messages,
which can provide useful information to diagnose and fix problems.
- If a migration process is started from a storage pool that does
not have the next storage pool identified in the hierarchy, a reclamation
process is triggered for the source storage pool. To prevent the reclamation
process, define the next storage pool in the hierarchy. For details,
see Setting up a storage pool hierarchy. As an alternative
to prevent automatic migration from running, set the HIGHMIG parameter
of the storage pool definition to 100.