Why is just one single session used for restoring the data during a Data Protection for Microsoft SQL Server VSS restore?
If you are performing a Microsoft Volume Shadow Copy Service (VSS) restore through the Data Protection for Microsoft SQL Server and the backupmethod parameter is specified to vss, only one single restore session is utilized at one time, even if the following conditions are met:
- RESOURCEUTILIZATION is set to a value larger than 1 (for the DSMagent)
- MAXNUMMP of DSMAgent node is larger than 1
- The data being restored is on more than 1 tape volume
The VSS processing will use the Tivoli Storage Manager Remote Agent service (DSMagent) when saving or restoring the data for the Data Protection SQL client. Since it is the DSMagent that is performing the VSS processing, the parameters in the dsm.opt file for the DSMagent will be utilized. For example, the RESOURCEUTILIZATION parameter from the client (DSMagent) options file is used, not the setting for the Data Protection for Microsoft SQL client.
From a Tivoli Storage Manager backup-archive client perspective, multiple restore sessions (based on RESOURCEUTILIZATION) are allowed only for no query restore operations in which the Tivoli Storage Manager server determines the files to be restored. A VSS restore cannot be "no-query" because the client builds the restore list (it is not based on a wildcard specification). Additionally, Data Protection for SQL will group the files during the VSS backup, restricting the VSS restore so that it does not support multiple restore sessions.
In order to run multiple restore sessions, legacy backup and restore should be considered.
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