How policy affects backup management on Data Protection for SQL Server

A Tivoli® Storage Manager policy determines how Data Protection for SQL Server backups are managed on Tivoli Storage Manager storage and on local shadow volumes when the environment is configured for VSS operations.

The Tivoli Storage Manager server recognizes and Data Protection for SQL Server as a node.

Data that is backed up to Tivoli Storage Manager storage from the Data Protection for SQL Server node is stored and managed according to settings that you specify in the Tivoli Storage Manager server policy.

The Tivoli Storage Manager policy manages the VSS backups that are placed in Tivoli Storage Manager server storage pools. The Tivoli Storage Manager server manages VSS backups.

If you use IBM® Tivoli Storage Manager for Copy Services and upgrade to Data Protection for SQL Server, with the license for Tivoli Storage Manager for Copy Services, you can store VSS backups to local shadow volumes.

Tivoli Storage Manager requires that sufficient storage space is available to create shadow volumes for VSS backup processing. Even when the VSS backup destination is the Tivoli Storage Manager server, storage space to create a shadow volume is still required temporarily.

The number of local backup versions that are maintained by the Tivoli Storage Manager server is determined by the value that is specified by the Tivoli Storage Manager server verexists parameter, which is defined in the copy group of the management class to which the local backup belongs. It is not necessary to allocate target sets when you use the VSS system provider. When you do not use the VSS system provider, the number of target volume sets that are allocated for local backups must be equal to the value of the verexists parameter. Target volume sets are not applicable to IBM XIV® Storage Systems.

For example, if verexists=3, then at least three sets of target volumes must be allocated for the backup to complete successfully. If only two sets of target volumes are allocated, the third and subsequent backup attempts fail. If more sets of target volumes exist than the number specified by the verexists parameter, these sets are ignored by the Tivoli Storage Manager server. A high number of local backup versions cannot be stored. If you want to have n number of local backup versions, set the verexists parameter to n + 1.

When you use the configuration wizard in the GUI, the VSSPOLICY parameter is set in the tdpsql.cfg file.

Depending on the policy management settings, you can reuse a logical unit number (LUN) for a new backup. When a backup is requested and the maximum number of versions is reached, the software deletes the oldest snapshot (backup) to make space for the snapshot. If the new request fails after the oldest snapshot is deleted, you have one less backup version than expected.

You must manage the policy for local backups to reconcile the local backup repository with the information that is stored on the Tivoli Storage Manager server. For example, if target volume LUNs that are used for a local backup are removed from the storage system, the information that represents the backup on the Tivoli Storage Manager server must be reconciled. Similarly, if a Tivoli Storage Manager server policy determines that a local backup copy is no longer needed, the local backup manager must free the target volume LUNs to the storage system. The local backup manager is released so that these LUNs can be used for future backup operations. Tivoli Storage Manager automatically detects when these situations occur and completes the reconciliation.