IBM Tape Library Data Server › Drive Allocation With the RMS Interface Configured › Drive Allocation for Non-specific Scratch Mount Requests

Drive Allocation for 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. 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.
   • If the RMS location is the default location, CA VM:Tape selects a scratch tape from the corresponding pool and location.
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. For more information about using this exit, see ALLOCATE User 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 RMS location was selected, CA VM:Tape moves the drives that are defined to be in the RMS location to the front of EDL.
   • If the selected 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 it 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. If the allocated drive is an RMS location, CA VM:Tape sends a request to the RMS 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.