The Data Facility Hierarchical Storage Manager (DFHSM) is an IBM program product that automatically manages DASD space. One way that DFHSM manages space is to migrate inactive data sets to another storage device in a compressed format, and then to recall the data set when it is needed. Another way it manages space is by releasing space from over-allocated active data sets. This second feature is based on the number of extents allocated to a data set. When a data set reaches a specified number of extents, DFHSM moves the data set to a migration volume, deletes the data set from the original volume, and reallocates the data set. This migrate-and-recall process releases unused space, reduces the number of extents, and compresses partitioned data sets. CA PMO detects this move and treats the data set in the manner described under the "Deleting and Reallocating" sections above, depending on whether the library is automatically managed or protected.
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