Logical volumes in a VTS are stored on physical stacked volumes after the host closes the logical volumes. Without the deletion of expired VTS logical volume data, the data that represents the contents of a logical volume on a physical stacked volume is not expired from the VTS point-of-view until the logical volume is rewritten or otherwise modified. This causes the VTS to continue managing the data as if it were still active, even though the user has actually scratched it. These “user-expired” logical volumes are maintained as active data by the VTS during reclaim processing. These volumes also needlessly consume physical stacked volume resources, thus requiring more physical stacked volumes in a VTS.
The deletion of expired logical volume data eliminates the need for the VTS to manage logical volume data that has already been expired at the host. At the same time, it provides a “grace period” during which the VTS continues to manage the data after the host has expired the data. The deletion times are associated with categories that have the Fast Ready attribute.
Additionally, a "hold" setting can also be associated with categories that have the Fast Ready attribute to restrict the usage of volumes with an unexpired expire time. Restricted volumes cannot be used to satisfy a mount request and cannot be moved to a different category until their expire time duration has elapsed. Starting with Release 2.1 of the TS7700, restricted volumes can be moved to a non-fast ready (private) category in case they were accidentally returned to scratch. Since volumes with an unexpired expire time cannot be used to satisfy a mount request, they are also excluded from the scratch volume category count in the DISPLAY SMS,LIBRARY command.
See IBM TotalStorage Enterprise Automated Tape Library (3494) Operator’s Guide and the TS7700 Customer Information Center for more information on defining the Fast Ready categories.