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Backup & recoveryPythonFixes series

Backup and cost control

The backup run is green and the bill is real. Three tiers decide whether the copy is cheap and whether it is true.

Quick reference

  • Backup: Volume snapshot (SNAP) · Object archive (ARCH)
  • Verify: Restore drill (DRILL) · Checksum (HASH)
  • Retire: Retention policy (KEEP) · Delete (DEL)

Request flow: Volume snapshot → Restore drill → Retention policy → Delete; Object archive → Checksum → Retention policy

Around it: Exit code (EXIT) · Cost report (COST)

Explained

Backup

A volume snapshot for the fast copy, and an object archive for the slow one. The snapshot is the one you restore today; the archive is the one you keep for the year. Both are useless until something proves them.

Verify

A restore drill for the path, and a checksum for the bytes. The drill opens the archive, lists the expected paths and fails on a missing one; the checksum catches a file that changed after it was written. The drawing runs from each backup node to its check, then both checks feed retention.

Retire

A retention policy and a delete step. The policy says what stays: seven daily, four weekly, twelve monthly. The delete step runs on a schedule, so the archive does not become the largest line on the invoice.

The flow

Snapshot to drill, archive to checksum, drill and checksum to retention, retention to delete. Two nodes per tier, five arrows, one exit code.

The honest caveat: verification costs time and compute, and a checksum is not a restore. The drill is the only tier that proves the data is readable.

The lesson: a backup is a process with three tiers, not a file in a bucket.

In one line

Take the copy, then test the copy. The copy that restores is the only one worth paying for.

Drill the archive

python3 restore_drill.py backup.tar

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