Place candidate data sets in priority order for migration

After performing class transitions and migrating data sets for extent reduction, DFSMShsm places the remaining candidates for migration in order by priority. DFSMShsm gives the highest priority for migration to rolled-off generation data sets. It gives second priority to non-rolled-off generation data sets that have been identified for early migration. These are the non-rolled-off data sets that exceed the number specified by the # GDG ELEMENTS ON PRIMARY attribute.

After the two highest priority groups, priority is assigned to all other data sets on the basis of size and age. The age, for migration priority purposes, is an eligibility age determined from the last-used date and the value of the PRIMARY DAYS NON-USAGE parameter. Small data sets must be eligible for a longer time to attain the same or higher priority as larger data sets.