Tivoli Header

Administrator's Guide


Setting Up a Tape Rotation

Over time, media ages, and the data on backup may no longer be needed. You can reclaim useful data on media and then reclaim and reuse the media themselves. When you set up expiration processing, you can determine when data is no longer needed. See File Expiration and Expiration Processing.

TSM policy determines how many backup versions are retained and how long they are retained. See Basic Policy Planning.

Deleting Data - Expiration Processing
Expiration processing deletes data that is no longer valid either because it exceeds the retention specifications in policy or because users or administrators have deleted the active versions of the data. See Running Expiration Processing to Delete Expired Files.

Reusing Media - Reclamation Processing
Data on tapes may expire, move, or be deleted. Reclamation processing consolidates any unexpired data by moving it from multiple volumes onto fewer volumes. The media can then be returned to the storage pool and reused.

You can set a reclamation threshold that allows TSM to reclaim volumes whose valid data drops below a threshold. The threshold is a percentage of unused space on the volume and is set for each storage pool. The amount of data on the volume and the reclamation threshold for the storage pool affects when the volume is reclaimed. See Reclaiming Space in Sequential Access Storage Pools.

Determining When Media Have Reached End of Life
You can use TSM to displays statistics about volumes including the number of write operations performed on the media and the number of write errors. TSM overwrites this statistical data for media initially defined as scratch volumes each time the media are reclaimed. For media initially defined as private volumes, TSM maintains this statistical data, even as the volume is reclaimed. You can compare the information with the number of write operations and write errors recommended by the manufacturer.

Reclaim any valid data from volumes that have reached end of life. If the volumes are in automated libraries, check them out of the volume inventory. Delete private volumes the database. See Reclaiming Space in Sequential Access Storage Pools.

Ensuring Media are Available for the Tape Rotation
Over time, the demand for volumes may cause the storage pool to run out of space. You can set the maximum number of scratch volumes high enough to meet demand by doing one or both of the following:

For automated libraries, see Setting Up and Managing a Volume Overflow Location for an Automated Library Device.

Write-once-read-many (WORM) drives can waste media when TSM cancels transactions because volumes are not available to complete the backup. Once TSM writes to WORM volumes, the space on the volumes cannot be reused, even if the transactions are canceled (for example, if a backup is canceled because of a shortage of media in the device).

Large files can cause even greater waste. For example, consider a client backing up a 12GB file onto WORM platters that hold 2.6GB each. If the backup requires five platters and only four platters are available, TSM cancels the backup and the four volumes that were written to cannot be reused.

To minimize wasted WORM media:

  1. Ensure that the maximum number of scratch volumes for the device storage pool is at least equal to the number of storage slots in the library.
  2. Check enough volumes into the device's volume inventory for the expected load.

If most backups are small files, controlling the transaction size can affect how WORM platters are used. Smaller transactions mean that less space is wasted if a transaction such as a backup must be canceled. Transaction size is controlled by a server option, TXNGROUPMAX, and a client option, TXNBYTELIMIT.


[ Top of Page | Previous Page | Next Page | Table of Contents | Index ]