This section contains information to be aware of when using magnetic disk devices for ADSM. The sections give pointers to additional information.
When you define a storage pool that uses disk random access volumes, you can choose to enable or disable cache. When you use cache, a copy of the file remains on disk storage even after the file has been migrated to the next pool in the storage hierarchy, for example, to tape. The file remains in cache until the space it occupies is needed to store new files.
Using cache can improve how fast a frequently accessed file is retrieved. Faster retrieval can be important for clients storing space-managed files. If the file needs to be accessed, the copy in cache can be used rather than the copy on tape. However, using cache can degrade the performance of client backup operations and increase the space needed for the ADSM database. For more information, see "The Use of Cache on Disk Storage Pools".
As client files expire, the space they occupy is not freed for other uses until you run ADSM's expiration processing.
Expiration processing deletes from the ADSM database information about any client files that are no longer valid according to the policies you have set. For example, suppose four backup versions of a file exist in ADSM server storage, and only three versions are allowed in the backup policy (the management class) for the file. Expiration processing deletes information about the oldest of the four versions of the file. The space that the file occupied in the storage pool becomes available for reuse.
You can run expiration processing automatically or by command. See "Running Expiration Processing to Delete Expired Files".
You can specify a maximum number of scratch volumes for a storage pool that has a FILE device type. When ADSM needs a new volume, ADSM automatically creates a file that is a scratch volume, up to the number you specify. When scratch volumes used in storage pools become empty, the files are deleted.
When you back up the database or export server information, ADSM records information about the volumes used for these operations in the volume history. ADSM will not allow you to reuse these volumes until you delete the volume information from the volume history. To reuse volumes that have previously been used for database backup or export, use the DELETE VOLHISTORY command. For information about the volume history and volume history files, see "Saving the Volume History File".