Scratch Pools - Overview

Table of Contents

Default Scratch Pools

A scratch pool is a repository of media that are available for use. When a data protection, synthetic full, or auxiliary copy operation requires new media, the system takes one from a scratch pool. Media may be:

  • Assigned to a scratch pool when they were imported and discovered in the CommCell.
  • Logically reassigned from one scratch pool to another scratch pool.
  • Returned to a scratch pool by the system when all of its data are pruned or deleted. (For additional information, see Media Recycling.)

Every library has a default scratch pool, which is automatically created when the library is configured. When the system creates a storage policy for the library (e.g., when the library or one of its drive pools is configured), the primary storage policy copy is associated with the default scratch pool. In addition, when you import new media into the library, this is the scratch pool to which they are assigned (unless you specify otherwise). You can create any number of additional scratch pools, and assign these to different storage policy copies that access the library. You can also designate a user-defined scratch pool as the default for the library. See Change the Scratch Pool Associated With a Storage Policy Copy  for step-by-step instructions.

New Scratch Pools

A scratch pool is a repository of media that are available for use. Every library has a default scratch pool, which is created when the library is configured. You can create any number of additional scratch pools, and assign these to different storage policy copies that access the library. You can also designate a user-defined scratch pool as the default for the library.

The ability to create scratch pools and assign them to specific storage policy copies enables you to ensure that critical operations always have the media that they need. For example, assume that you regularly back up both a file server containing mission-critical data and a number of user PCs. You may want to prevent situations in which data secured from less important user PCS use up all available media, causing vital data protection operations on file server to fail. You can do this by creating a scratch pool specifically for the storage policy copies that conduct data protection operations on file servers. You can, if necessary, delete these non-default scratch pools.

You can move media between scratch pools. In the example above, if you noticed that the supply of media in the scratch pool dedicated to the file server was getting low, you could logically reassign media from another scratch pool to the file server pool.

You can also verify the media to confirm whether the media information displayed in the CommCell Console matches the OML in the media.

Low Watermarks

You can also establish a low watermark for each scratch pool. This parameter represents the minimum number of media that should be available inside the library for the scratch pool at all times. If the number of available media in the scratch pool falls below the low watermark, the system logs a message in the Event Viewer and generates the MediaAgents (Insufficient Storage) alert, if configured. You can view the status of media available in the scratch pools by generating the Scratch Pool Report.

The low watermark for all user created scratch pools in the CommCell can be established in the Default low-water mark for newly created Scratch Pools option established in the Service Configuration tab of the Media Management Configuration dialog box in the Control Panel. If necessary, you can modify the low watermark for the individual scratch pools. (See Specify the Minimum Number of Media in a Scratch Pool for step-by-step instructions.)

When you establish a low watermark, consider the media requirements of all operations (e.g., data protection operations, auxiliary copies, synthetic full backups) that draw from the scratch pool. The low watermark should be high enough to ensure that you will be notified of the need for more media while there are still enough media available to allow running operations to complete. For example, if the operations that access a particular scratch pool regularly fill two media every week, you might set the low watermark at three. This way, you will be alerted every week to add more media to the scratch pool while it still contains sufficient media to handle its normal operational load.

Related Reports

Scratch Pool Report

The Scratch Pool Report provides a list of the contents and low watermarks of scratch/cleaning pools.