One consequence of TSM’s “Progressive Incremental” approach is that objects which are no longer needed are still stored in the database and on media (volumes), in addition to objects that are still needed. If TSM let this condition continue indefinitely, the quantity of disk storage needed to store backups would exceed a reasonable level and would eventually fill up the ExaGrid appliance. The TSM reclamation process prevents the infinite growth of backup data.
ExaGrid recommends setting the reclamation threshold for all storage pools to 100% and then defining reclamation thresholds and schedules in either Administrative Schedules to finely tune reclamation for a specific storage pools or in Server Maintenance Schedules to broadly define when reclamation will run for all data backed up by the server.
In either case, reclamation should be run daily. A key part in planning your backups to an ExaGrid System must include accommodations for reclamation. Reclamation will free up disk space on your ExaGrid System consumed by expired objects within volumes.
To perform a reclamation operation, your TSM server must access your ExaGrid System. This process will use ExaGrid System resources that might otherwise be used to land, deduplicate and/or replicate your backups.
TSM Space Reclamation Process
TSM Space Reclamation is a process of identifying tape files that meet threshold requirements then moving the unexpired objects off the tape file candidate to another tape file. Here’s an example of how this works.
- In this example, all volumes are fully occupied by client data.
- As time passes by, data ages and expires. Space is (logically) freed up on the volumes.
- The space reclamation process consolidates and shifts the client data onto one physical volume which is then expired.
- The space that was reclaimed onto another volume has freed enough space to create an empty volume.
For more information on using TSM and ExaGrid together for better TSM backups, download a copy of the ExaGrid and TSM Best Practices Guide from our TSM Resource Page.