What is Hierarchical Storage Management?
Hierarchical Storage Management is a strategy for data storage in which data is distributed across multiple levels of storage media, based upon the access requirements of the data.
Data that must be accessed frequently will be stored in primary storage. Primary storage usually consists of DASD, NAS, or SAN devices. Primary storage should always be online, and for that reason is is sometimes called online storage.
Data which may be accessed infrequently can be stored in secondary storage. Secondary storage usually consists of DVD and optical drive jukeboxes, but can also refer to magnetic tape jukeboxes. Secondary storage can be bought online without operator intervention. Secondary storage is sometimes referred to as near line storage.
Data which is not expected to be necessary can be stored in tertiary storage. Tertiary storage usually consists of magnetic tapes. Tertiary storage usually must be loaded by an operator, and for that reason tertiary storage is usually called offline storage.