Specifying the WAIT option

When DFSMShsm requests a tape allocation, an exclusive enqueue is obtained on the task input/output table resource (SYSZTIOT). This exclusive enqueue stays in effect until the tape device is allocated or the request fails. Therefore, if you specify the WAIT option, all DFSMShsm functions are suspended until a device is allocated to the task that holds the exclusive enqueue.

The WAIT option is recommended only for:

Environments that use JES3 to manage tapes.
Because of main device scheduling, you should specify INPUTTAPEALLOCATION(WAIT) so that the DFSMShsm allocation request can be put into the queue for device availability. Input tape requests that occur during the day need to be honored, because they will usually be requests to recall or recover data sets.

You may want to use OUTPUTTAPEALLOCATION(WAIT) if you are doing interval migration with some data sets migrating directly to tape in a JES3 environment. Interval migration runs on an hourly schedule throughout the day, and you want DFSMShsm to be able to obtain a tape device through the main device scheduler. For more information about interval migration, see z/OS DFSMShsm Storage Administration.
Environments that use esoteric unit names to restrict the use of some tape devices to DFSMShsm processing. You can use the WAIT option because a tape device should usually be available.

If you specify . . .	Then . . .
SETSYS INPUTTAPEALLOCATION (WAIT) SETSYS OUTPUTTAPEALLOCATION (WAIT) SETSYS RECYCLETAPEALLOCATION (WAIT)	The dynamic-allocation function of MVS™ waits for a tape device allocation before returning control to DFSMShsm.

Note: Ensure that there are enough tape devices available for the number of tasks currently running. What can be perceived as a DFSMShsm-not-running condition can occur because of the exclusive enqueue that MVS puts on SYSZTIOT while awaiting completion of tape device allocation.