Reorganizing the control data sets

Reorganization of the control data sets is extremely dangerous, and reorganization should be performed only if one of the following conditions exists:

When you need to move a control data set to a new DASD volume.
When you need to increase the space allocation of a control data set, as indicated by the ARC0909E or ARC0911E messages.

DFSMShsm issues these messages when the threshold requested by the SETSYS MONITOR command has been exceeded. You can display the current status of the control data sets with the QUERY CONTROLDATASETS command. Status is reported in the ARC0148I and ARC0948I messages. To reorganize the control data sets, use the Access Method Services (AMS) EXPORT and IMPORT commands. To move the control data sets to another volume or to increase their space allocations, use the AMS DEFINE, REPRO, and DELETE commands.

Attention: Do not attempt to reorganize your control data sets while DFSMShsm is running on any processor that uses those control data sets.

Several topics should be considered when reorganizing the control data sets. The primary consideration is that DFSMShsm must be shut down in all processors that have access to the control data sets. No job in any processor should attempt accessing the control data sets during their reorganization. The starter set job, HSMPRESS, provides a sample job for reorganizing control data sets. VSAM SHAREOPTIONS parameters for control data sets provides detailed information about protecting the control data sets from damage when they are reorganized in a multiple DFSMShsm-host environment.

After a control data set is reorganized, expect to see performance degraded for a period of about three weeks while CA and CI splits occur. The 44-character keys for most of the DFSMShsm records are time-stamped to distribute the I/O activity as evenly as possible. When increasing the space allocation, attempt a large enough increase so that reorganization is not required for another 3–6 months, based on your current growth rate.

You can significantly reduce the need to reorganize the DFSMShsm control data sets by enabling the CA reclaim function for them. For more information, see the topic about reclaiming CA space in z/OS DFSMS Using Data Sets.