If you are planning to use migration for sequential-access
storage pools, consider the time that is required to mount tapes into
drives and whether collocation is enabled.
When you define migration criteria for sequential-access storage
pools, consider:
- The capacity of the volumes in the storage pool
- The time that is required to migrate data to the next storage
pool
- The speed of the devices that the storage pool uses
- The time that is required to mount media, such as tape volumes,
into drives
- Whether operator presence is required
- The number of concurrent migration processes
If you decide to migrate data from one sequential-access storage
pool to another, ensure that:
- Two drives (mount points) are available, one in each storage pool.
- The access mode for the next storage pool in the storage hierarchy
is set to read/write.
For information about setting an access mode
for sequential-access storage pools, see Defining storage pools.
- Collocation is set the same in both storage pools.
For example, if collocation is set to NODE in the first storage pool,
then set collocation to NODE in the next storage pool. If collocation
is set to FILESPACE in the first storage pool, then set collocation
to FILESPACE in the next storage pool.
When you enable collocation
for a storage pool, the server tries to keep all files on a minimal
number of volumes. The files can belong to a single client node, a
group of client nodes, a client file space, or a group of file spaces.
For information about collocation for sequential-access storage pools,
see Keeping client files together using collocation.
- You have sufficient resources (for example, staff) available to
manage any necessary media mount and dismount operations. (This is
especially true for multiple concurrent processing, For details, see Specifying multiple concurrent migration processes.)
More mount operations occur because the server attempts to reclaim
space from sequential-access storage pool volumes before it migrates
files to the next storage pool.
If you want to limit migration
from a sequential-access storage pool to another storage pool, set
a high, high-migration threshold, such as 95%.
For information
about setting a reclamation threshold for tape storage pools, see Reclaiming space in sequential-access storage pools.
There is no straightforward way to selectively migrate data for
a specific node from one sequential storage pool to another. You can
use the MOVE NODEDATA command to move file spaces for a node from
one storage pool to another. See Moving data belonging to a client node.