When cache is enabled, the migration process leaves behind duplicate copies of files after the server migrates these files to the next storage pool in the storage hierarchy. Using cache can improve the speed with which the server retrieves some files. Consider enabling cache for space-managed files that are frequently accessed by clients.
If space is needed to store new data in the disk storage pool, cached files are erased and the space they occupied is used for the new data.
For the best performance for client backup operations to disk storage pools, do not use cache.
When cache is disabled and migration occurs, the server migrates the files to the next storage pool and erases the files from the disk storage pool. By default, the system disables caching for each disk storage pool because of the potential effects of cache on backup performance. If you leave cache disabled, consider higher migration thresholds for the disk storage pool. A higher migration threshold keeps files on disk longer because migration occurs less frequently.
If fast restores of active client data is your objective, you can also use active-data pools, which are storage pools containing only active versions of client backup data. For details, see Active-data pools.
To enable cache, specify CACHE=YES when defining or updating a storage pool.