What is a storage device hierarchy?

A storage device hierarchy consists of a group of storage devices that have different costs for storing data, different amounts of data stored, and different speeds of accessing the data.

DFSMShsm uses the following three-level storage device hierarchy for space management:

Level 0, including DFSMShsm-managed storage devices at the highest level of the hierarchy, contains data directly accessible to you.
Level 1 contains data sets that DFSMShsm has moved from level 0 volumes.
Level 2 contains data sets that DFSMShsm has moved from level 1 or level 0 volumes.

Storage devices at the lower levels of the hierarchy, level 1 and level 2, contain data that DFSMShsm has compressed and optionally compacted into a format that you cannot use. Devices at this level provide lower-cost-per-byte storage and usually slower response time.