Before a storage pool can be used to store data, volumes must be assigned to the pool. Volumes are assigned differently depending on whether the pool is a random access storage pool or a sequential access storage pool.
Volumes in random access storage pools must be prepared for use (formatted) and then defined. See Chapter 10. "Managing Storage Pool Volumes" for information about formatting and defining volumes.
You can define volumes in a sequential access storage pool or you can specify that ADSM dynamically acquire scratch volumes. You can also use a combination of defined and scratch volumes.
Use defined volumes when you want to control precisely which volumes are used in the storage pool. Using defined volumes may be useful when you want to establish a volume naming scheme for ADSM volumes. See Chapter 10. "Managing Storage Pool Volumes" for information about defining volumes.
Use scratch volumes to allow ADSM to dynamically acquire a volume when needed and dynamically delete the volume when it becomes empty. For example, you might want to use scratch volumes to avoid the burden of explicitly defining all of the volumes in a given storage pool.
ADSM tracks whether a volume being used was originally a scratch volume. Scratch volumes that ADSM acquired for a primary storage pool are deleted from the ADSM database when they become empty. The volumes are then available for reuse by ADSM or other applications. For scratch volumes that were acquired in a FILE device class, the space that the volumes occupied is freed by ADSM and returned to the file system.
Scratch volumes in a copy storage pool are handled in the same way as scratch volumes in a primary storage pool, except for volumes with the access value of offsite. If an offsite volume becomes empty, ADSM does not immediately return the volume to the scratch pool. The delay prevents the empty volumes from being deleted from the database, making it easier to determine which volumes should be returned to the onsite location. The administrator can query ADSM for empty offsite copy storage pool volumes and return them to the onsite location. The volume is returned to the scratch pool only when the access value is changed to READWRITE, READONLY, or UNAVAILABLE.