As backup data is usually a copy of live data, it's usually necessary to retain this data so you can restore it should the original be damaged in some way, or for compliance purposes. The retention period for live data is governed by the useful life of the data itself. Once the data has passed its useful lifecycle, it should be moved to archive or backup media and stored in keeping with the organisation's retention and compliance policies.
When considering the target media for both categories of data, the time interval that is acceptable between requests for the data retrieval and when the data actually arrives must be established. This will determine what media the data is written to for backup data, and what archiving policies are enforced for live data.
Once the recovery time limit or objective has been established, then the type of data store should be the cheapest available choice that meets this limit while also meeting other security, resilience and compliance criteria. The following are examples of media that meet various time limits:
- 10 seconds: Online SATA data store such as archive volume
- 30 seconds: Massive array of idle disks (MAID) energy-efficient data store
- 10 minutes: Tape drive (in library) or virtual tape library (VTL)
- 4 hours: Tape drive (on site, outside library)
- 8 hours: Offsite tape facility
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