Caching in disk storage pools

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.

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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.

Using cache has some important disadvantages:
  • Using cache can increase the time required for client backup operations to complete. Performance is affected because, as part of the backup operation, the server must erase cached files to make room for storing new files. The effect can be severe when the server is storing a very large file and must erase cached files.

    For the best performance for client backup operations to disk storage pools, do not use cache.

  • Using cache can require more space for the server database. When you use cache, more database space is needed because the server has to keep track of both the cached copy of the file and the new copy in the next storage pool.
  • If you want to use caching, you cannot also enable shredding for that disk storage pool. See Securing sensitive client data for more information about shredding.

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.