Glossary

Archive — Borg's word for one backup run stored in a repository; a named, frozen state of your files.

Backup — a copy of your data that survives the loss of the original, including losses you cause yourself: separate, versioned, automatic, tested.

Blob — restic's word for one chunk of stored data inside a pack file.

Check — a verification pass over a repository: structural (restic check) or full read-and-decrypt (--read-data). Finds damage while it's still fixable.

Chunk — the piece a file is split into before storage. Deduplication works at chunk level: identical chunks are stored once, however many files or snapshots use them.

Deduplication — storing each unique chunk exactly once. The reason a month of daily snapshots costs barely more than one.

Dead man's switch — a monitoring service that alerts you when an expected success signal stops arriving. Catches the failures where nothing is left running to complain.

Forget — restic's command that marks snapshots outside your retention policy. Their data is removed by prune.

Key (Borg) — the cryptographic key material for a Borg repository, separate from the passphrase. Export it (borg key export) and store it elsewhere, or a reinstall can orphan a healthy repository.

Pack — a file inside a restic repository containing many encrypted blobs, stored as one unit.

Prune — actually deleting data no surviving snapshot references, reclaiming the space. In Borg, the reclaim step is compact.

Repository — the place backups live: a folder on a backup drive, a server, or cloud storage, holding the encrypted, deduplicated data plus its index. Not meant to be browsed by hand.

Restore — reading files back out of a snapshot or archive into ordinary folders. The entire point.

Retention policy — the rule for how much history to keep (--keep-daily 7 --keep-weekly 4 ...). Applied by forget/prune (restic) or prune (Borg).

Snapshot — restic's word for one backup run: the state of the backed-up folders at that moment.

Sync — keeping two places identical (Dropbox, iCloud). Protects against a lost device; faithfully propagates deletions and corruption. Not a backup.

3-2-1 rule — three copies of what matters, on two different kinds of storage, one of them off-site.