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Two questions determine your backup strategy: how much work may you lose, and how long may you be down? Those are RPO and RTO. The 3-2-1 rule is the practical translation: three copies, on two kinds of storage, one of them off site and unreachable from the network.
The terms
- RPO — how much work lost
- The time between two backups. A daily backup means that at worst you redo a day of work.
- RTO — how long down
- The time to being operational again. Often longer than expected: restoring takes time and the environment has to be right again.
- 3-2-1
- Three copies of your data, on two different kinds of storage, one of them off site.
- Offline copy
- A backup that cannot be reached from the network. This is what makes ransomware harmless.
What is wrong in practice
- Never restored
- A backup that has not been tested is an assumption. Test a full restore at least once a year.
- Everything in one place
- A NAS in the same room is not a second location. Fire and theft hit both copies.
- Cloud is not a backup
- A synchronised folder copies the encryption or the deletion too. Versioning or a separate backup is needed.
- Forgotten systems
- The AS/400, the director’s laptop, the webshop at an external party. What is not on the list does not get restored.
Decide the two numbers first — how much work and how much downtime is acceptable — and only then choose the solution. The other way round gets expensive without getting better.
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