You can choose whether to automatically reclaim SMS-managed generation data sets (GDSs) that are in deferred roll-in state or turn off that function.

By default, SMS automatically reclaims GDSs when a new generation of a generation data set does not get rolled into the GDG base for various reasons. Any job that creates a new (+1) generation causes SMS to automatically reclaim the GDS. When SMS reclaims a GDS, it reuses a GDS that is in a deferred roll-in state. This reuse could destroy a new generation created by the first job if another job overlays it.

For example, job A creates A.B.C.G0009V00 but the roll-in does not occur because the address space abnormally ends. Because generation G0009V00 did not get rolled in, jobs that refers to A.B.C (+1) attempt to recreate G0009V00. SMS gets a failure due to the duplicate data set name when it tries to catalog the new version of G0009V00. However, SMS detects that this failure occurred because a previous roll-in of G0009V00 did not occur. Consequently, SMS reuses the old version of G0009V00. Any data that was written in this old version gets rewritten.

Warning: Usually, GDS reclaim processing works correctly when you rerun the abending job. However, if you accidentally run another job before rerunning the previous job, data loss might occur. If this situation occurs in your installation, you might want to turn off automatic GDS reclaim processing. If you turn off GDS reclaim processing, you will need to manually delete or use the IDCAMS ROLLIN command to roll in the generation that did not get rolled-in. Note that the OPTION to either turn "on" GDS reclaim processing or to turn it "off" applies to the entire system. It is not possible to set this OPTION to a particular value just for one JOB or STEP. Different systems in a sysplex may set their own value for this option but this may lead to unpredictable results.

Because GDS reclaim applies to an existing dataset, attributes of the reclaimed GDS (for example, space allocation, SMS constructs, and volume) cannot be changed. The reclaimed GDS will have the attributes of the deferred GDS.

Related reading: For information on changing the setting for GDS reclaim processing, see the z/OS DFSMSdfp Storage Administration. For information on the access method services commands for generation data sets, see the z/OS DFSMS Access Method Services Commands.