Specifying the NOWAIT option

When you specify the NOWAIT option, dynamic allocation does not wait for a tape device to become available. Dynamic allocation returns control to DFSMShsm immediately, either with a tape device allocated or with a failure indication if no tape device is immediately available. Therefore, other DFSMShsm data-movement functions can continue to process data while the task requiring tape is waiting to reissue the allocation request. The NOWAIT option is recommended for:

JES2 environments.
Because a JES2 system does not preschedule devices, DFSMShsm has an opportunity in such a system to obtain the needed tape devices when it requests them.
Environments that hold some tape devices offline so the operator can vary the devices online when DFSMShsm issues the ARC0381A message.

If you specify . . .	Then . . .
SETSYS INPUTTAPEALLOCATION (NOWAIT) SETSYS OUTPUTTAPEALLOCATION (NOWAIT) SETSYS RECYCLETAPEALLOCATION (NOWAIT)	The dynamic-allocation function of MVS™ returns control to DFSMShsm and does not suspend system activity while a device is being allocated.

If the allocation request fails because no devices are available, DFSMShsm repeats the request six more times. If a tape device cannot be allocated after seven tries, DFSMShsm issues a message asking the operator either to cancel the request or to repeat the set of requests.

If a tape device can become available within a reasonable time, the operator should reply with RETRY. DFSMShsm then repeats the request seven more times. If a tape device is still not allocated, DFSMShsm again asks the operator whether it should cancel the request or repeat the request. A reply of CANCEL fails the DFSMShsm task immediately.

At some sites, some device addresses are defined to the system only as spare addresses and not as actual devices. When DFSMShsm issues a tape allocation request and all tape devices are in use, the allocation request is not failed with a reason of no units available. Instead, the allocation message (IEF238D) is issued, and the only tape device addresses listed are the spare addresses. If the device addresses are only spares, the operator should reply CANCEL to this message. If this is the first time the operator has replied CANCEL to message IEF238D, DFSMShsm issues an ARC0381A message to verify the request that it discontinue trying to find a target tape device.