The Backstore Engine › Starting, Stopping, and Restarting the Backstore Engine

Starting, Stopping, and Restarting the Backstore Engine

The default name for this engine is SVTSAS. This name can be changed to any name other than SVTSIO and SVTn by modifying the SubAddressSpaceName attribute in the Startup Options Section of the VTPARMS parmlib member. The Backstore Engine and the Virtual Device Engine share the same started task procedure, but use step names of SVTnPT and SVTnVm respectively (where n = the subsystem number and m = 1 to 8).

When the Subsystem is started, the SVTS task is initialized first. The SVTS task then starts the SVTSAS tasks, including the Backstore Engine.

When the Subsystem is stopped, the SVTS task stops the SVTSAS tasks, including the Backstore Engine, and then stops itself.

All console commands issued to CA Vtape are issued to the SVTS started task. Subsequent communications between the SVTS and SVTSAS started tasks by CA Vtape are done using system MODIFY (F) commands.

If the Subsystem detects a Restart Backstore console command, the following actions are taken:

• All Externalization tasks in progress are gracefully stopped, releasing the tapes and tape devices.
• All Recall tasks in progress are gracefully stopped, releasing the tapes and tape devices.
• The Externalization Subgroup Queues are held.
• The SVTSAS.SVTnPT address space is stopped and restarted.

If Subgroup Automation is active, no manual intervention is required. If Subgroup Automation is not active, the only manual intervention required is to release the desired groups so Externalization can resume. For the Recalls in progress, the requester is kept in active status waiting for data and, after a few minutes, the internal Missing Interrupt Handler (MIH) support restarts the Recall. As soon as the Backstore Tape is positioned at the same point where it was before, the requester automatically continues its processing.

If you do not want to wait for MIH to restart the pending Recalls, you can issue the SVTn MOUNT console command for each Virtual Volume whose Virtual Device is in Mount Pending status.

Note: For more information about this command, see the chapter “Console Commands”.

Important! If the Backstore Engine is cancelled or forced when Externalization has tapes mounted, these tape should be excluded from additional processing by using the SVTn SET BACKstore=EXCVOL,VOLume=volser console command. The cancel or force will prevent the last file sequence number used from being saved. If these tapes are remounted, the Backstore Engine will need to read these tapes sequentially to find the last file sequence number. This could cause a significant delay in Externalization as first the PRIMARY tape is mounted and read sequentially, followed by the DUPLEX tape, if duplexing is active.