A VSS backup uses Microsoft Volume Shadow Copy Service technology to produce an online snapshot (point-in-time consistent copy) of SQL data.
VSS backups eliminate the need for the server or file system to be in backup mode for an extended period of time. The length of time to perform the snapshot is usually measured in seconds, not hours. In addition, a VSS backup allows a snapshot of large amounts of data at one time because the snapshot works at the volume level.
VSS backups can be stored on local VSS shadow volumes, or, when integrated with Tivoli® Storage Manager, in Tivoli Storage Manager server storage. Both of these storage destinations require that sufficient space be available for the snapshot.
When sufficient space is available for the snapshot, VSS backups stored locally on VSS shadow volumes are directly accessible by the system.
Restoring locally managed VSS backups is fast because the SQL data is not transferred from Tivoli Storage Manager server storage over the network.
When you run VSS backups and store data on Tivoli Storage Manager server storage, sufficient space is temporarily required on local snapshot volumes. This space is used to hold the snapshot until transfer to the Tivoli Storage Manager server is complete. After the data transfer to the server is complete, the snapshot volume is released. The space can be reused.
If you also store VSS backup locally, in addition to Tivoli Storage Manager server storage, and the maximum number of local backup versions to be maintained is reached, the oldest local backup version expires to create the new snapshot for the backup to Tivoli Storage Manager server storage. The maximum number of local backup version to be maintained is set in the Tivoli Storage Manager policy.
For data backed up to local VSS shadow volumes, the snapshot backup is on the shadow copy volume.
For data backed up to both VSS shadow volumes and Tivoli Storage Manager server storage, a local snapshot backup is run and the data on the local snapshot volume is sent to the Tivoli Storage Manager server. The local snapshot volume is retained as a local backup after the transfer to the Tivoli Storage Manager server is complete.