Immutable backup (and the 3-2-1 rule)
termIT supportsecurity
A backup copy that cannot be altered or deleted for a defined period, even by an administrator - achieved through storage-level object lock, genuinely offline media, or a separate trust domain with its own identity.
The classic 3-2-1 rule - three copies, two media, one off-site - predates an adversary who hunts backups, and every copy it describes can sit behind the same administrative credential. The missing clause is that one copy must fall outside the blast radius of the credentials that manage production, because if a domain administrator can delete the backups then a domain administrator compromise deletes all of them regardless of how many there are. Retention should also outlast plausible dwell time, or every surviving copy already contains the intrusion.
Also known as: 3-2-1, object lock, worm storage, offline copy, air-gapped backup