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Data set reorganization (REDUCEXT) used with StopX37/II

As part of the recovery process, you might need to add an additional volume to save the job from abending. This process, referred to as a volume switch, reorganizes a multivolume data set back to a single volume.

The Data set reorganization utility (REDUCEXT) uses the IBM IDCAMS DCOLLECT and DFDSS control cards to automate the process of consolidating extents by using a single job. This job examines your DASD farm and consolidates appropriate files with multiple extents. IDCAMS DCOLLECT determines which files are candidates for extent reduction, and then DFDSS performs the actual reduction. DCOLLECT is used because of its speed in collecting the required data.

SMS-managed and non-SMS-managed data sets require different approaches. Only one DFDSS copy is issued for an SMS-managed data set. This copy consolidates extents and moves the data set to a different SMS-managed volume that is appropriate for the data set. For a non-SMS-managed data set, the data set is first moved to a work volume (specified by the WK=parameter), where the extents are consolidated. By default, this location is a temporary location, and a second copy is issued to return the data set to the originating volume. If the data set does not need to be returned to the original volume, you can specify the ONEWAY parameter. The work volume is required for non-SMS data sets and can be used for an SMS-managed data set if only one volume exists in the storage group (and no other storage group can be made available).

By default, DFDSS will not process data sets for extent reduction if these data sets have a high-level qualifier of SYS1. To include these data sets manually, you can code a parameter of SYS1.

You can use the SIM parameter to obtain a list of the candidate data sets for extent reduction prior to executing. A similar capability is offered with the NORUN parameter, which generates COPY requests for the DFDSS NORUN mode. This feature could be used to identify data sets that are ineligible for processing because of outstanding ENQueues.

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