DFHSM is the Hierarchical Storage Management product, that manages the stored location of active and inactive files for you, by "migrating" from (for example), fast DASD, slow DASD, or to tape, "recalling" the file when it is referenced. The site's DASD Administrator sets the rules for when migration occurs. In spite of the sentiments of the button, HSM is one of the most powerful tools in the MVS world, and nothing like it exists for unix/linux/windows in 2005