SUTMYN Automated Tape Library › Recommendations and Considerations › Drive Allocation for Saved Tape Mounts

Drive Allocation for Saved Tape Mounts

1. When CA VM:Tape receives a saved tape 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 queries the LMS if the tape is inside an LMS-controlled device. The location of the tape determines which tape drives will be selected for allocation.
3. 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.

   Note: For more information about the ARM command, see the Command Reference Guide.

4. 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. For more information about using this exit, see ALLOCATE User Exit.
5. 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.

   Based on the tape’s location, the following processing occurs:

   • If the tape is inside the LMS location, CA VM:Tape moves the drives inside the LMS location to the beginning of the EDL. Drives that are outside the LMS are exempted from the EDL.
   • If the tape is outside the LMS location, CA VM:Tape exempts the drives in the LMS locations and moves the drives in the NONARM location 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.

6. 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.
7. If the allocated drive is an LMS location, CA VM:Tape sends a request to the LMS to mount the tape 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.