DFSMShsm migrates the data sets that are candidates for extent
reduction and schedules recalls for those same data sets. During the
migration, DFSMShsm moves only the valid data from the data sets.
Therefore, when the data sets are recalled into fewer extents, they
may occupy less space.
Note, also, the following rules:
- If the data set is eligible for a class transition with data movement
(DSS Copy/Delete) and extent reduction, then only the class transition
will be performed.
- If the data set is eligible for a class transition without data
movement (i.e. only the management class is changing) and extent reduction,
then extent reduction will be performed after the class transition
(again, with only the management class changing, without data movement).
- If the data set is eligible for a class transition, migration
and extent reduction, then only the migration will be performed.
- If the data set is eligible for extent reduction only, then the
data set will be processed after all data sets eligible for extent
reduction and class transition, and after all the data sets eligible
for extent reduction and migration have been processed.