SUTMYN Automated Tape Library › Recommendations and Considerations › Drive Allocation With Non-specific Scratch Mount Requests

Drive Allocation With Non-specific Scratch Mount Requests

1. When CA VM:Tape receives a scratch mount request, it scans the device list looking for any drive that can satisfy the request. Options specified by the user issuing the request and the site-defined defaults determine which drives are eligible. CA VM:Tape places the drives that are eligible in an EDL. Each time an EDL is built, CA VM:Tape starts the EDL with a different drive to allow for uniform use of your hardware. There is one EDL for each request.
2. CA VM:Tape reduces the EDL by submitting the reducible drives in the EDL to LMS through the QUERY ALLOCATE function. These drives can be exempted if LMS site-specified allocation control rules apply. The rules are supplied by the allocation domain table statements ALLOCATE, DEVICES, and DOMAIN, as documented in the SUTMYN LMS Systems Guide.

   The ARM REDUCE STEP command determines whether this reduction step is applied. In addition, the ARM REDUCE raddr command determines which individual drives participate in this step. For more information about the ARM command, see the Command Reference Guide.

3. CA VM:Tape calls the ALLOCATE user exit. The ALLOCATE user exit allows a site to change the order of drives in the EDL and select which drives to allocate based upon information about each request. When you use the ALLOCATE user exit, CA VM:Tape calls it after constructing the EDL. See ALLOCATE User Exit for more information about using this exit.
4. CA VM:Tape applies its drive ordering to the EDL.

   Note: Set the return code to zero in your ALLOCATE user exit to bypass CA VM:Tape’s drive ordering and instead have CA VM:Tape allocate drives as returned by the user exit.

   CA VM:Tape reorders the drives based on the tape’s location, and performs the following processing:

   • If the LMS location is the default location, CA VM:Tape moves the drives that are defined to be in the LMS location to the front of EDL.
   • If the default location is NONARM, those drives are moved to the beginning of the EDL.

   If a drive is initially reserved for the user requesting the mount, and is also the tape’s location, CA VM:Tape moves the drive to the front of the EDL.

5. Beginning with the first drive in the EDL, CA VM:Tape proceeds through the list of drives until it finds a free drive. If none of the drives are available, the process pends for 30 seconds and CA VM:Tape goes through the EDL again. This process continues, based on the time specified on the REMINDER record, until a drive becomes available and CA VM:Tape allocates a drive.
6. Based on the options specified on the mount command and the allocated drive, CA VM:Tape selects a tape pool from which it can select a scratch tape. If the scratch pool facility is not configured, then all tapes belong to a general scratch pool and CA VM:Tape always selects tapes from the general scratch pool.
7. If the allocated drive is an LMS location, CA VM:Tape sends a request to the LMS for a scratch tape from the corresponding pool, and requests the tape to be mounted on the allocated drive.

   If the allocated drive is NONARM, CA VM:Tape sends a message to the tape operator to mount the tape on the allocated drive.