Tape rotation, as it applies to TSM, refers to the ongoing circulation of tapes through the storage management process. Once TSM selects an available tape, the tape is used and eventually reclaimed according to its associated policy. TSM tape rotation does not generally consist of an administrator backing up a given data set to tape and then repeatedly overwriting that tape with the same data set.
TSM manages the data on tape and optical disk media, but administrators manage the physical media. Administrators can manage media themselves, with some help from TSM, or they can extend media management capabilities by using a removable media manager. Regardless of the methods or tools used, managing media typically leads to setting up a media rotation. A media rotation is a media management scheme that captures the data retention and media reuse goals of the administrator. It requires that administrators create policy to expire aged (and now invalid) data, reclaim valid data onto new media, and reuse the physical media.
As part of managing the data on volumes, administrators tune expiration processing and data reclamation.
TSM places information into the volume history log about tapes used for database backups and exports (for disaster recovery purposes). The process for reusing these tapes is slightly different than the process for reusing tapes containing client data backups.
The data on a tape or optical disk volume changes over time as a result of:
Figure 7 illustrates a typical life cycle for scratch tapes. Scratch tapes are recommended. The private or scratch status of tapes is determined when devices are configured; specifically, when storage pools are created for the device media. When working with new media this is important because even before TSM knows about tapes, an implication exists that tapes have a status of either scratch or private as a result of the storage pool defined for the media when the device was configured for TSM.
Figure 7. Simplified View of Tape Rotation
Numbers in the following text (such as (1)) refer to numbers in Figure 7.