The MWE subparameter specifies the number of NOWAIT MWEs from each user address space that are kept in CSA until they are completed.

The MWE subparameter can be set to 0 if DFSMShsm is solely responsible for making storage management decisions. The benefit of setting the MWE subparameter to zero (the default is four) is that the CSA an MWE consumes is freed immediately after the MWE has been copied into DFSMShsm ’s address space, making room for additional MWEs in CSA. Furthermore, if DFSMShsm is solely responsible for storage management decisions, the loss of one or more NOWAIT MWEs (such as, a migration copy that is not being deleted) when DFSMShsm is stopped could be viewed as insignificant.

The benefit of setting the MWE subparameter to a nonzero quantity is that MWEs remain in CSA until the function completes, so if DFSMShsm stops, the function is continued after DFSMShsm is restarted. The default value of 4 is sufficient to restart almost all requests; however, a larger value provides for situations where users issue many commands. MWEs are not retained across system outages; therefore, this parameter is valuable only in situations where DFSMShsm is stopped and restarted.

Restartable MWEs are valuable when a source external to DFSMShsm is generating critical work that would be lost if DFSMShsm failed. Under such conditions, an installation would want those MWEs retained in CSA until they had completed.

The decision for the storage administrator is whether to retain NOWAIT MWEs in CSA. No method exists to selectively discriminate between MWEs that should be retained and other MWEs unworthy of being held in CSA. Figure 1 shows the three storage limits in the common service area storage.

Figure 1. Overview of Common Service Area Storage