The 3-2-1 Backup Rule: A Practical Guide

What is the 3-2-1 rule?

The 3-2-1 rule is a simple, proven way to make sure you can always recover your data. Keep three copies of your data, on two different types of storage, with one copy offsite.

Applying it, step by step

1. Count your copies. Your live data is copy one. Add at least two backups, so one failure never leaves you without a copy.
2. Use two types of storage. For example, a local disk or appliance plus a UK cloud service. Different types of storage are unlikely to fail in the same way at the same time.
3. Move one copy offsite. A cloud backup in a UK data centre protects you from fire, flood, theft and anything else that could affect your premises.

The modern upgrade: 3-2-1-1-0

Ransomware has changed the picture. Attackers now look for backups as well as live data, so many organisations add two more ideas to the rule:

• One immutable copy, which cannot be changed or deleted for the period you set.
• Zero errors, achieved by checking backup reports and testing restores regularly.

Common mistakes

• Keeping every copy on the same network
• Treating file sync (such as OneDrive or Google Drive) as a backup
• Backing up the data but not the systems that run it
• Never testing a restore

A checklist

• Three copies of every critical system
• Two different storage types
• One offsite copy, held in the UK
• One immutable copy
• Restores tested at least twice a year

See also our guides to testing your restores and ransomware recovery.