Tivoli Storage Manager for Windows Administrator's Guide


Setting Up a Tape Rotation

As time passes, backups age, and the data on backup media becomes unimportant. Administrators are responsible for reclaiming any residual useful data on media and then reclaiming and reusing the media itself. This cycle is often thought of in terms of the media rotation and to a great extent, media rotation is driven by the rate at which data expires and becomes invalid. Administrators determine the rate at which data becomes invalid when they set up expiration processing. See File Expiration and Expiration Processing.

Expiration is controlled by TSM policy. The policy determines how many backup versions TSM retains and policy determines how long backup versions are retained. As backups age, policy determines when they can be deleted by expiration processing. See Basic Policy Planning.

Deleting Data - Expiration Processing

Managing data in a media rotation typically involves setting up and running expiration processing regularly to delete data that is no longer valid either because it exceeds the data retention specifications in policy or because users or administrators have deleted the active versions of the data. Administrators determine how long the data on media is valid, and how often TSM runs expiration processing, when they set up policy. See Running Expiration Processing to Delete Expired Files.

Reusing Media - Reclamation Processing

Administrators determine when to reuse media by the way they setup reclamation processing. Reclamation processing is a function whose role is to reclaim valid data from aging volumes and reuse the media. Data on tapes may expire, move, or be deleted. Reclamation processing consolidates any unexpired data by moving it from many aging volumes onto fewer new volumes. The media can then be returned to the storage pool and reused. For each different type of device configured with the Device Configuration Wizard, the wizard creates a storage pool for the device media.

Setting Up a Reclamation Threshold

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

When all valid data either expires or is moved to another volume, the volume is available for reuse (after any time delay specified by the REUSEDELAY parameter for the storage pool). The empty volume becomes a scratch volume if it was initially a scratch volume.

Determining When Media has Reached Its End of Life

Administrators can use the QUERY VOLUME command to help determine when media has reached its end of life. TSM displays statistics including the number of write operations performed on the media and the number of write errors. For media initially defined as scratch volumes, TSM overwrites this statistical data each time the media is reclaimed. For media initially defined as private volumes, TSM maintains this statistical data, even as the volume is reclaimed. Administrators can compare the information with the number of write operations and write errors recommended by the manufacturer.

Administrators must reclaim any valid data from volumes that have reached end of life. If the volumes are in automated library devices, check them out of the volume inventory. Private volumes must be deleted from the TSM database. See Reclaiming Space in Sequential Access Storage Pools.

Drive Cleaning Operations

You can use TSM to manage tape drive cleaning. For automated library devices, you can automate cleaning by specifying the frequency of cleaning operations and checking a cleaner cartridge into the library's volume inventory. TSM mounts the cleaner cartridge as specified. For manual library devices, TSM issues a mount request for the cleaner cartridge. See Cleaning Drives.

Note:TSM drive cleaning management is not intended to be used with SCSI library devices with built-in automated cleaning functions.

Ensuring Media is Available for the Tape Rotation

An organization's demand for media grows in proportion to the growth of data, so as data grows, administrators may need to occasionally increase the number of volumes available to TSM. Initially, the media available to TSM is determined when a device is configured and a storage pool is defined for the device. When the demand for TSM volumes exceeds the maximum number for the storage pool, the storage pool can run out of space.

Administrators can set the maximum number of scratch volumes high enough to meet demand by doing one or both of the following:

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

Managing a Supply of Volumes in a Write-Once-Read-Many (WORM) Library Device

Administrators managing devices with write-once-read-many (WORM) drives must maintain a sufficient supply of volumes in the library device to prevent wasting media. Media is wasted 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 cannot complete because of a shortage of media in the device, TSM cancels the backup. The WORM volumes to which TSM had already written are wasted because they cannot be reused.

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 TSM wrote to are wasted and cannot be reused.

To minimize wasted WORM media:

  1. Ensure that sufficient volumes are available in the library device.
  2. 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 device.
  3. Check a sufficient number of volumes into the device's volume inventory to accommodate 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.


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