Product Components › Typical Mount Scenario › Drive Allocation for Mount, Allocate, and Reserve Requests

Drive Allocation for Mount, Allocate, and Reserve Requests

1. When CA VM:Tape receives a scratch or saved tape mount request, or an allocate or reserve 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 eligible drive list (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.

   If the ALLOCATE user exit is not configured, skip the next step.

2. 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.
3. CA VM:Tape applies standard drive ordering to the EDL.

   Note: Set the return code to zero in your ALLOCATE user exit to bypass standard drive ordering. Otherwise, set the return code to one (1) to instruct VMT to apply standard drive ordering of the EDL.

   During standard drive ordering, CA VM:Tape selects drives for allocation based on the order in which they appear in the EDL. CA VM:Tape puts the drives in the default location (NONARM if you are not using an ARM product) at the beginning of the EDL. Additionally:

   • If you use the STAM facility, for manual mounts, CA VM:Tape reorders the EDL to put STAM preferred drives at the beginning of the list. For more information about STAM, see "Shared Tape Allocation Manager (STAM) Facility."
   • If a drive was initially reserved for the user requesting the mount, CA VM:Tape moves it to the front of the EDL.
4. 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.
5. For mount requests, CA VM:Tape sends a message to the tape operator to mount the tape on the allocated drive.