DFSMShsm moves only data and not the entire allocated space when it migrates and recalls or backs up and recovers data sets. If you allocate more space for a partitioned data set than the data requires, DFSMShsm releases both the unused space and the used space that is no longer valid when it migrates and recalls or backs up and recovers the data set. Furthermore, if you have specified secondary extents, when DFSMShsm recalls or recovers the data set to a DFSMShsm-managed volume, it allocates only the amount of space that the data requires. DFSMShsm retains user information in partitioned data set directories.