Task allocation of volumes

Device management controls and monitors the allocation of resources requested by the user (devices, volumes, files) depending on the volume usage mode.

For tapes and private disks, the following modes exist:

• "DMS"
  for all DMS accesses (using commands SECURE-RESOURCE-ALLOCATION, CREATE-FILE, ADD-FILE-LINK, COPY-FILE...)

• "SPECIAL"
  special applications (e.g. utility routines INIT, VOLIN, FDDRL ...)

In addition, the following usage mode is provided for tapes:

• "WORK"
  for DMS work tapes, see commands SECURE-RESOURCE-ALLOCATION, ADD-FILE-LINK in the “Commands” manual [27]

Task-exclusive allocation:

A volume cannot be allocated by more than one task at a time. All other task allocation requests for the same volume within the same system or from other systems are rejected.

Exception: exclusive allocation requests (SECURE-RESOURCE command) of batch tasks wait until the volume has been released.

Task-shareable allocation:

A volume can be allocated by more than one task at a time. The only volumes which can be allocated as task-shareable are disks in USE-MODE=DMS (public and private disks).

Allocation types for private volumes and other resources:

• Allocation of tapes

  Tapes are always allocated as task-exclusive; task-shareable allocation is not possible. The system determines whether the tape is only to be allocated or if it is actually to be used. If it is only allocated, i.e. other tasks have no access to the tape but I/O operations do not occur, the operator is requested via a premount message to carry out device allocation if the tape is not recognized as being mounted. If, however, the tape is to be used for I/O operations, the operator is informed of this via a mount request.

• Allocation of private disks

  Private disks are allocated as task-shareable for DMS operation (usage mode DMS) by default. Task-exclusive allocation is only possible via an appropriate reservation (SECURE).

  Disks for the usage mode SPECIAL are allocated as task-exclusive.

  The operator can use the disk parameter USER-ALLOCATION to specify which task allocation is permitted for a disk (usage mode DMS).

  USER=*EXCL enables a disk to be allocated as task-exclusive only (with SECURE-RESOURCE-ALLOCATION DISK= ...,ALLOC=*EXCL). The disk allocated in this way is then only available for this task. Any attempt to allocate this disk as task-shareable is rejected.

  USER=*SHARE enables the disk to be allocated for all DMS and SECURE requests exclusively as task-shareable. All task-exclusive allocation requests for this disk are rejected.

  USER=*ALL enables the disk to be allocated for all task-shareable and task-exclusive DMS and SECURE requests. This is only valid for initial allocation of the disk. If the disk is allocated as task-exclusive, all other allocation requests for this disk from other tasks are rejected.

  USER=*NO enables the disk to be reserved by a user. This setting is made automatically by the system in the event of: /CHANGE-DISK-MOUNT
UNIT=mn/*VOLUME(vsn), ACTION=*CANCEL or if a remount message is answered with tsn.N.

• Allocation of other resources

  All allocation requests for devices (tape/disk devices, etc.) are allocated as task-exclusive without operator intervention.