Backup (3-2-1 Rule)
Backups protect against data loss; the 3-2-1 rule improves resilience.
Updated: 2026-03-05
Definition
Backups are copies of data stored separately so it can be restored after deletion, corruption, or ransomware.
The 3-2-1 rule means: 3 copies, 2 different media, 1 offsite copy.
Key points
- Test restores regularly
- Keep offline/immutable copies when possible
- Backups are a core ransomware defense
Common mistakes
- Never testing restore procedures.
- Keeping backups online and writable by compromised accounts.
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