Overview of two-pass automatic primary space management

DFSMShsm-managed volume space management is performed in two passes, as follows:

1. Pass 1 deletes the appropriate data sets, releases unused space, performs fast subsequent migration, and determines which data sets on the volume are candidates for migration, class transitions, or extent reduction. Performs class transitions with management class changes only.
2. Pass 2 processes the candidates for extent reduction, transitions data sets, and migrates data sets until the low threshold of occupancy is reached.