Backup

A backup is a copy of data kept separately so it can be restored after loss — hardware failure, a mistaken deletion, a bad migration, ransomware.

Replication and snapshots are not backups. They faithfully reproduce whatever happened, including the deletion, and they usually live on the same infrastructure that a real disaster removes. A backup is a separate copy, ideally in a separate place, that a compromise of production cannot reach or overwrite.

The only meaningful measure of a backup is a completed restore. Untested backups fail at the moment of use with impressive regularity — an incomplete dump, a missing encryption key, a process nobody has run since the person who wrote it left. Restore one on a schedule, and know how long it takes, because that duration is your actual recovery time.