The ARCMDEXT installation exit receives control whenever a data set fulfills the selection criteria for the level 0 volume being managed, but before the data set migrates or transitions. It is called when DFSMShsm processes a level 0 volume or an individual data set through any of the following:

• HMIGRATE command
• MIGRATE command
• Automatic primary space management
• Interval migration
• On-demand migration
• Class transitions

The input data structure provides flags that identify the type of volume migration function under which the exit was invoked.

This exit is called for both system- and non-system-managed data sets that are eligible for migration or extent reduction. A flag (DS1SMSFG) in the data set VTOC entry indicates whether the data set is system managed. For multivolume data sets, the exit is called for only the first volume. For system-managed data sets, the input data structure provides the associated management class.

An indicator in the ARCMDEXT parameter list indicates that this invocation is for a data set migrating by way of a data set command, not by way of a volume migration.

This exit is not called for data sets moving between migration volumes.

You must write ARCMDEXT to be reentrant.