See Step 12: Creating the DFSMSrmm control data set for information on creating the DFSMSrmm control data set, including information on how to calculate DASD space for the control data set, placement of the control data set, and allocating space for the control data set. We recommend that you ensure that CA Reclaim is not disabled and that you allocate the DFSMSrmm control data set with enough secondary space, so that the DFSMSrmm control data set can grow as you add new resources such as volumes and data sets. Also, allow for enough planned free space in the DFSMSrmm control data set to allow for growth and any known new-volume requirements. However, at some time, the allocated space in the DFSMSrmm control data set will fill up and new extents are allocated and used as long as there is free DASD space available. The DFSMSrmm control data set can grow in size within the limits imposed by VSAM and DFSMS.

Use the LISTCAT output from IDCAMS to check the details of the DFSMSrmm control data set and the RMM LISTCONTROL CNTL subcommand to list the calculated percentage used for the DFSMSrmm control data set. DFSMSrmm calculates the percentage of the DFSMSrmm control data set used by checking the High Used RBA and High Allocated RBA that the LISTCAT output shows. This percentage does not take into account any available embedded free space, nor does it take into account the number of used extents or the additional free space that might be available to extend the DFSMSrmm control data set.

Decide how you will monitor and report on the DFSMSrmm control data set space used. By using the information available to you, including your predicted tape usage, decide if the DFSMSrmm control data set is large enough or needs to be reallocated. Decide on your own thresholds, and check regularly to ensure they are used to trigger corrective action. Although you can reorganize the DFSMSrmm control data set to recover free space, do not do this regularly. Ensure your DFSMSrmm control data set is large enough and can grow as required to avoid the need to reorganize it regularly.