anonymous
2010-10-28 16:20:40 UTC
HSM mean Hierarchical System Management.
HSM is essentially the automatic movement of data between media, the media type used depending on when it was last accessed.
The most common HSM setup is where there is online storage, near-line storage and offline storage.
The hard disks are usually used for online storage, the optical media are used for near-line storage and tape is normally used for offline storage.
When data is not accessed for long time, it’s automatically moved from the online storage to the near-line storage.
The Systems keep a marker in the directory structure, so that user can still see the file when it has been moved into near-line storage.
When the user tries opening the file, it will automatically be copied from near-line storage to online storage.
When the file is in the offline storage, in the near-line storage there’s a reference that contain the number of the offline tape where the file is on.
If the user tries opening this file, a request is sent to the system administrator and the file can be recovered from tape.
The factor to determine the choice of storage media used, depends on the length of time you want your data to remain intact, and also the speed at which you want to recover it.
One important thing to remember with archiving systems is the stored data's format.
The data might be held 10 or 15 years in the offline storage, but you will need an appropriate, software and hardware to read it.