ITPEC FE Morning October 2020 Question 57

Back up related files once the whole series of updates to them has finished — so that the backup holds them in a consistent state.

When related data are spread over several files, one update job usually changes all of them. A backup taken partway through could hold some files from before the update and others from after it, and restoring it would give data that contradict each other. Waiting until the series of updates is complete makes the backed-up files agree, so a restore returns a usable state.

Answer (b)

Why not others:

• •(a) — after the first full backup, changes to data that are updated only occasionally would never be backed up again; every change must be covered, for example by periodic full backups plus incremental or differential ones
• •(c) — deleting the backups of data removed from the disk leaves no copy at all; low-use data should be moved to archive media, not destroyed
• •(d) — overwriting the same media each time keeps only one generation: if a backup run fails or copies data that are already corrupted, the last good copy is lost, so several generations should be kept on separate media

Key rule: A backup is only useful if it can be restored to a correct state: take it where related data agree, cover every change, and keep more than one generation.

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