Backup

Backup is the process of copying a collection of data, the object, from “primary” to “secondary” storage for the purpose of recovery in the event of failure. Its complement is Recovery, the process invoked on failure or other requirement to return the contents of the collection to primary storage. To be useful for recovery, the source data image needs to be in a consistent state during the backup. The copy should provide a non-volatile point of retrieval. In addition, a data object may have multiple copies or recovery points. Failure causes may be logical, physical, accidental or intentional resulting in loss or inaccessibility of the original data.

The primary storage is typically disk. The secondary storage is typically magnetic tape, often called removable media because it is easy to transport to an alternate location. Today, disk/tape combinations and remote disks may serve as secondary storage in addition to other media forms. An alternate location or site is required in the event of primary site destruction or that the site becomes unavailable. In most cases, the legal or insurance test of backup "validity" requires a combination of the ability to recover from the media and physical storage of the media at a specified minimum distance form the primary site.