JES3 considerations

For the recall of SMS-managed data sets, JES2 and JES3 appear to be the same. However, for non-SMS-managed data sets, the following differences can occur when DFSMShsm is used on a single DFSMShsm-host or a multiple DFSMShsm-host configuration in a JES3 environment using the benefits of JES3 data set reservation as provided by JES3 setup.

Volumes are considered in terms of data set pools, volume pools, and general pools. The general pool, configured by DFSMShsm, is the default pool that contains primary volumes that are online and permanently resident or reserved and that have the automatic recall attribute. From this set, volumes are selected for undirected recall.
For migrated data sets, JES3 associates the requested data set with a subset of five or fewer candidate pool volumes supplied by DFSMShsm. JES3 treats the data set as a multiple-volume data set.
For data sets that have not migrated, JES3 associates the requested data set to the serial number of the primary volume on which the data set resides. DFSMShsm prevents migration of the data set for today and three more days.
DFSMShsm recalls the migrated data set to a specific volume serial number in the candidate volume list when the data set is opened or to the best candidate primary volume in the subset of five or fewer pool volumes when the data set is allocated.

This discussion is concerned only with the function of delaying migration. Associating migrated data sets with volumes for recall is described in Recall, a discussion of automatic recall for non-SMS-managed data sets.

During the post-scan phase, JES3 calls its locate module to locate the cataloged data sets.When the JES3 locate routine finds a primary volume serial number for a requested data set in the computing system catalog, JES3 associates the specified data set with that volume serial number. Asynchronously with the JES3 locate routine, DFSMShsm passes a management work element (MWE) to prevent migration of the requested data set for up to three days (default value) by recording the primary volume serial number and a prevent-migration date in the MCDS data set (MCD) record. The prevent-migration date is the last day that migration is prevented. If the job does not run within a prevent-migration period, the prevent-migration date expires, and the data set can migrate automatically or by command.

A JES3/DFSMShsm migration window exists between the asynchronous processing of the JES3 locate routine and the DFSMShsm management work element. If migration of the data set occurs in the JES3/DFSMShsm migration window, DFSMShsm modifies the MCD record so that the recall of the migrated data set occurs to that primary volume serial number that was returned to JES3. If you enter a command to migrate a data set associated with a volume that has a current prevent-migration date, DFSMShsm fails the command. A message is issued to indicate that JES3 has an outstanding request for the data set, and migration is prevented until the prevent-migration date has expired.

The prevent-migration period is a default value of 3 in the management communication vector table (MCVT). The default value is added to the current date to create the prevent-migration date and the hold-volumes date in the MCD record. You can change this value. Although the value can range from 0–255, the value should be consistent with the maximum time a job can exist in JES3 before it is run.

JES3 directed-recall and prevent-migration requests are processed as DFSMShsm commands. In a multiple DFSMShsm-host environment, these requests may not be processed until the completion of a command that is currently being processed. Normally, the delay has little effect on the time required to process the JES3 request. However, some performance degradation may be noticed if the DFSMShsm command processor is waiting for the availability of a resource.

JES3 considerations

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