The Backstore Engine › Allocation Logic - CA MIM or IBM GRS Support › Contention Over Backstore Tapes

Contention Over Backstore Tapes

The following contention scenarios involve the same Backstore Tape:

• A Recall is attempted and the Backstore Tape is in use by Recycle on any system. Expected action: The Backstore Tape will be released as soon as the current Virtual Volume being processed is completed.
• A Recall is attempted and the Backstore Tape is in use by Externalization on the same system. Expected action: The Recall will be queued under the Externalization task and the queue will be processed in FIFO order. The queue can be displayed by using the SVTn DISPLAY BACKSTORE console command.
• A Recall is attempted and the Backstore Tape is in use by Externalization on a different system. Expected action: The Recall task will enqueue the cartridge using SYSZVOLS and will wait until the resource is released.
• A Recall is attempted and the Backstore Tape is in use by another Recall recalling the same Virtual Volume on any system. Expected action: The Recall task will issue message SVTnV0400I and wait for the other Recall to complete. The job that requested the Recall will access the Virtual Volume from the DASD buffer as soon the enqueue on SYSZVOLS for the Backstore Tape is released.
• A Recall is attempted and the Backstore Tape is in use on the same system for another Recall. Expected action: The Recall will be queued under the in-progress Recall task and the queue will be processed in FIFO order. You can display the queue by using the SVTn DISPLAY BACKSTORE console command. If several Recalls are started at the same time, one or more of them may have originally started as separate tasks, but as soon the situation is detected CA Vtape will automatically requeue all the Recalls under one task.
• A Recall is attempted and the Backstore Tape is in use on a different system for another Recall. Expected action: The Recall task will enqueue the cartridge using SYSZVOLS and will wait until the resource is released.
• An Externalization is attempted and Recycle is in progress for the same group or subgroup in any system. Expected action: Externalization will not start until Recycle finishes or is stopped.
• An Externalization is attempted and Recall is using the Backstore Tape on the same system. Expected action: Message SVTnPX132W will be issued and the Externalization task will be rescheduled.
• An Externalization is attempted and Recall is using the Backstore Tape on a different system. Expected action: The Externalization task may enqueue the Backstore Tape using SYSZVOLS and wait until the resource is released. If not, message SVTnPX132W will be issued and the Externalization task will be rescheduled.

By design, each Externalization subtask on each system uses its own Backstore Tapes for Externalization. There is no potential contention for the same Backstore Tape between Externalization tasks on the same or different systems.

Note: Setting up one subsystem as both the Externalization Server and as the Recall Server eliminates all cross-system contention for Backstore Tapes. By propagating the SVTSX and SVTRCYCL QNAMES across systems, contention for Backstore Tapes with Recycle can be eliminated.