StorageTek Nearline Automated Cartridge System › Drive Allocation With the HSC Interface Configured › 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 HSC, checking if the requested tape is inside an HSC-controlled device. The location of the tape determines which tape drives will be selected for allocation.
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.

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

   • If the tape is inside the ACS location (a library storage model, or LSM), CA VM:Tape requests the HSC to return a list of drives, in order of proximity to the requested tape.
   • If the tape is outside the ACS location, CA VM:Tape exempts the drives in the ACS 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 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 ACS location, CA VM:Tape sends a request to the HSC 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.

   Note: If the library storage module that contains the tape is already in manual mode, CA VM:Tape displays a message on the tape drive display panel that asks the operator to mount the tape and indicates the panel row and column number of the LSM where the tape is located.