Reclamation:
As new files are backed up and expiration runs, entries for older files will be deleted from the database. Although the entries are deleted, the actual data for these files will not be immediately removed from the backup media. In the case where the backup media device is a tape, we will end up with portions of the tape used and portions of the tape no longer needed because it contains expired data. As backups and expiration continue, tapes will eventually reach a point where a significant amount of the data stored on them is no longer needed. Unfortunately, since tape is sequential access media, there is no way to simply “fill in” the empty space with new data from backups.
TSM deals with recovering this unused space on sequential media through a process called reclamation. The software allows you to set an allowable threshold for unused space on Sequential media. When expired data on a tape hits the reclamation threshold, the reclamation process takes the data from the tape that is still useful (active and inactive data) and moves it to an empty tape (a scratch tape). The expired data is discarded, and since the tape has no useful information after the reclamation process, it is returned to the scratch pool to be reused at a later time. Note that the reclamation process is a tape-to-tape copy process. In order to reclamation to occur, the software must have two tapes mounted simultaneously; the one being reclaimed and the new scratch tape to which the active and inactive data is being written.
Syntax:
Reclaim stgpool pool_name threshold=number duration=minutes offsitereclaimlimit=no of volumes(for offsite volumes)
Expiration:
Periodically, the server will search through its database to determine files which have more versions than are allowed or which are older than are allowed. This process of finding these files which are older than retention policy allows is called expiration. When the entries for these files are found, they are deleted from the database.
Syntax:
expire inventory duration=minutes
Retention policy:
In a traditional server based backup solution, the tape operators control how long to keep the backups. When a full backup gets too old, they simply put the tape back into the rotation and overwrite the data on it. This methodology will not work with TSM. Since it’s the TSM server software that’s mounting tapes, the software must be able to determine when a backup is too old and delete it from the system. The TSM server controls how long a backup is kept by establishing a retention policy. At the TSM server, the administrator establishes a policy about the number of backup versions to keep and how long to keep them. Then, when the TSM server finds that it has backups that no longer needs, it deletes the entries for those backups from the database.