Hierarchical Storage Management (HSM)

Hierarchical Storage Management (HSM)
HSM (Hierarchical Storage Management) provides continuous online backup functionality.
It combines hard disk technology with the cheaper and slower optical or tape
jukeboxes. The HSM system dynamically manages the storage and recovery of files,
which are copied to storage media devices that vary in speed and cost. The faster media
holds the data that are accessed more often, and the seldom-used files are stored on the
slower devices, or near-line devices The storage media could
include optical disks, magnetic disks, and tapes. This functionality happens in the background
without the knowledge of the user or any need for user intervention.
HSM works, according to tuning based on the trade-off between the cost of storage
and the availability of information, by migrating the actual content of less used files to
lower-speed lower-cost storage, while leaving behind a “stub,” which looks to the user like it contains the full data of the migrated file. When the user or an application accesses
the stub, the HSM uses the information in the stub to find the real location of the
information, and then retrieve it transparently for the user.

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