Assigning a higher priority to virtual tape library volumes during restore/retrieve

Content

Because VTL volumes are typically smaller than real tape volumes, more volume mounts are required to restore and retrieve data; especially large data objects. This causes the server to select real tape volumes over VTL volumes. One of the selection criteria that the Tivoli Storage Manager server uses is the number of volumes it will need to mount from each storage pool. The storage pool that requires the fewest mounts is given priority over other storage pools. This selection criteria has caused some undesirable results when VTLs are used for the primary storage pool, and the corresponding copy storage pool uses real tape. Because VTL volumes typically are smaller and require more mounts than real tape volumes, preference is given to the real tape volumes in the copy storage pool.

However, because of the performance benefit of using a VTL, restore and retrieve is typically faster than that of real tape devices, regardless of how many VTL volume mounts are required.

To have the Tivoli Storage Manager server bypass the check that compares the number of volume mounts and select VTL volumes over real tape volumes regardless of how many VTL volumes are required to be mounted, add the following option to the server options file. The option must be present during server startup:

IGNORENUMVOLSCHECK YES

This option is most useful when a VTL primary storage pool is being backed up to a real tape device copy storage pool and the copy storage pool volumes are being selected over the VTL volumes.

Attention:

Important notes:

1. This option is temporary and will be removed in a future release of Tivoli Storage Manager. The server will be enhanced to provide full VTL support, which will include the ability to recognize a VTL and assign the appropriate volume selection priority.
2. This option also affects the volume selection during server processes such as migration, reclamation, and move and copy commands.