You can arrange storage pools in a storage hierarchies, which consist of at least one primary storage pool to which a client node backs up, archives, or migrates data. Typically, data is stored initially in a disk storage pool for fast client restores, and then moved to a tape-based storage pool, which is slower to access but which has greater capacity. The location of all data objects is automatically tracked within the server database.
You can set up your devices so that the server automatically moves data from one device to another, or one media type to another. The selection can be based on characteristics such as file size or storage capacity. A typical implementation might have a disk storage pool with a subordinate tape storage pool. When a client backs up a file, the server might initially store the file on disk according to the policy for that file. Later, the server might move the file to tape when the disk becomes full. This action by the server is called migration. You can also place a size limit on files that are stored on disk, so that large files are stored initially on tape instead of on disk.
For example, your fastest devices are disks, but you do not have enough space on these devices to store all data that needs to be backed up over the long term. You have tape drives, which are slower to access, but have much greater capacity. You define a hierarchy so that files are initially stored on the fast disk volumes in one storage pool. This provides clients with quick response to backup requests and some recall requests. As the disk storage pool becomes full, the server migrates, or moves, data to volumes in the tape storage pool.
Another option to consider for your storage pool hierarchy is IBM® 3592 tape cartridges and drives, which can be configured for an optimal combination of access time and storage capacity. For more information, see Controlling data-access speeds for 3592 volumes.
Migration of files from disk to sequential storage pool volumes is particularly useful because the server migrates all the files for a group of nodes or a single node together. This gives you partial collocation for clients. Migration of files is especially helpful if you decide not to enable collocation for sequential storage pools. For details, see Keeping client files together using collocation.