Key takeaways
- 3-2-1 means three copies of your data, on two different types of storage, with one copy off-site.
- Against ransomware, make at least one copy offline or immutable.
- A backup is only proven when you have test-restored it.
The rule in one sentence
The 3-2-1 backup rule means keeping three copies of your data, stored on two different types of media, with one copy kept off-site. It means no single failure, such as a dead drive, a stolen laptop or a fire, can wipe out every copy.
Each number explained
| Number | Means | Example |
|---|---|---|
| 3 copies | The live data plus two backups | Server + local backup + cloud backup |
| 2 media types | Backups on different kinds of storage | A backup appliance and cloud storage |
| 1 off-site | At least one copy away from the premises | Encrypted cloud backup |
Adding ransomware protection
Ransomware can encrypt any backup it can reach. That is why many IT providers now add a further requirement: at least one copy should be offline or immutable, meaning it can't be changed or deleted for a set period. The Australian Cyber Security Centre's Essential Eight also lists regular, tested backups as one of its eight essential strategies.
Applying it in a small office
- Back up servers and important PCs nightly to a local device.
- Replicate that backup to encrypted cloud storage.
- Back up Microsoft 365 separately, because its recycle bins have time limits.
- Set up alerts for failed backups.
- Test a restore every quarter and record the result.
For medical practices, see backup planning for accreditation, or our managed backup service.
Common questions
Is cloud backup enough on its own?
It covers the off-site copy, but restoring a whole system over the internet can be slow. A local copy gives faster recovery.
Does 3-2-1 apply to Microsoft 365?
Yes. Your Microsoft 365 data is one copy; a separate backup outside your tenant gives you an independent second copy.
Reviewed by Graham Graieg and Dane, Triad Networking Services. See our editorial policy.
Sources
General information only, current as of 6 October 2026.