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(12) Backup snapshots

Backup snapshots

The AFS system allows a snapshot to be taken of a volume at any point in time. The main purpose of this is to 'freeze' a volume so that it can be transferred to backup medium (tape etc.) in a self-consistant state. Backup snapshots are very quick and efficient. Only files changed since the last backup snapshot are actually duplicated on disk.

We generate backup snapshots each night just after midnight (00:10). These are then copied to the long-term backup system, but the snapshot remains online until overwritten the next night. This means that an accidentally deleted or corrupted file is actually still online in last night's snapshot. Users can mount their own home volume backup snapshot (readonly) and retrieve files without needing administrative priviledges. It is confusing to leave the backup volume mounted permanently.

The procedure is:
fs mkmount ~/YESTERDAY user.myname.backup

YESTERDAY is now a read-only copy of your entire account as of last midnight. Files can be copied out of it with all the usual Unix tools, but nothing can be modified

fs rmm ~/YESTERDAY (remove the temporary mountpoint)

Backup snapshots are migrated to tape each night. We take full backups monthly (kept for 12 months) and incremental backups nightly (kept for 31 days).

backup-snapshots.src last modified Jan 24, 2005

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