DFSMShsm initializes the date-last-referenced field of supported data sets in the data set VTOC entry when the volume is first processed for volume space management. When a data set is opened after that, the open routine writes the current date in the date-last-referenced field. DFSMShsm refers to the date-last-referenced field and the PRIMARY DAYS NON-USAGE and LEVEL 1 DAYS NON-USAGE attributes to determine if a data set is eligible for space management. Since the date-last-referenced is set when a data set is opened, a data set that is open for several days can be eligible for migration shortly after it is closed. Allow extra days in the management class parameters for this situation.
If the date-last-referenced field is zero during volume space management, DFSMShsm places the current date into the field. Zeros in the date-last-referenced field mean that volume space management has never processed the data set.
For the majority of ways that DFSMShsm recalls can be initiated, the recall is considered a reference to the data set, so the date-last-referenced field of the data set is set to the current date. As a result, you can preschedule work by recalling data sets that will be required during a later work session. DFSMShsm normally does not automatically migrate these recalled data sets before you can use them.
The date-last-referenced field is not updated when a data set is moved as a result of a class transition.