Mark Fernandes
Dell's Dr. Mark Fernandez

In the last installment of this blog, we discussed the Hierarchical Storage Management system or HSM, and discussed migration and recall. Migration and recall are determined by policies set within the HSM. Policies may be triggered by such file characteristics as the time since the file was last used, for example. In this example, a file that has not been used in some period of time is “migrated” to a lower storage tier, freeing up that valuable space on the high-speed HPC storage, for example. Two key things to remember are (1) the file or data still appear to be in the original location and (2) the file or data are actually moved to a different location and are subject to “recall” as needed. Note that a copy of the file or data is NOT made. In general, there remains only one copy, maximizing use of all available storage. Hence, an HSM is NOT a Backup System and should not be confused with one.

Backup is an entirely different, mature and extensive industry unto itself. In general, in the backup world, the terms used to describe the functionality of the Backup System are “backup” and “recover” (or “backup” and “restore”). In a Backup System, one or more copies of a file are created and safely secured.

Similarly, an Archive System is neither an HSM nor a Backup System. IMHO, an Archive System is different from a Backup System in that a Backup System can be mindless and typically (tries to) back up everything. In contrast, an Archive System contains files or data that have value as determined by humans and which have been specifically placed there, possibly for safe use by others. Similar to an HSM and a Backup System, an Archive System uses carefully chosen terms to describe its functions: “archive” and “access”.

In the next part of this blog, we will continue to describe the distinctions between an HSM, Backup and Archive. If you have comments or can contribute additional information, please feel free to do so.