Data sets migrate in priority order from the primary volume until the low threshold of occupancy is reached or until the age of the oldest remaining data set is less than the minimum migration age.
Example: If a primary volume has a low threshold of occupancy of 80% and a minimum migration age of four days, DFSMShsm migrates data sets until at least 20% of the volume is available or until all data sets not referred to within the last three days have migrated.