The 3-2-1 Rule
Scope: the classic shape of a backup setup that survives real life. It's a rule of thumb, not a law — understand the reasoning and you can bend it sensibly.
The rule
Keep 3 copies of anything that matters, on 2 different kinds of storage, with 1 copy somewhere else entirely.
- 3 copies — the original, plus two backups. Two backups sounds paranoid until the day you restore from backup #1 and find it corrupt; backup #2 is what makes that an annoyance instead of a funeral.
- 2 kinds of storage — say, your computer's SSD and an external hard drive, or a home server and a cloud bucket. Two drives of the same batch, bought the same day, in the same enclosure, can share the same defect and the same bad week.
- 1 copy off-site — fire and theft take the whole building. The off-site copy is the one that makes those recoverable.
A concrete, ordinary setup
Nothing exotic is required. A setup a mortal can actually maintain:
| Copy | Where | How |
|---|---|---|
| Original | Your laptop/desktop | — |
| Backup 1 | External drive or home server | Nightly restic backup (this guide) |
| Backup 2 (off-site) | Cloud storage, or a drive kept at a relative's house / office | restic to a cloud repository, or a second drive you swap weekly |
The "drive at a relative's house" version is real and respectable: two external drives, one plugged in, one off-site, swapped whenever you visit. The catch is the swap cadence — the off-site copy is only as fresh as your last visit. Cloud storage fixes the cadence and charges rent; a relative's shelf is free and charges discipline.
What counts as "different storage" in 2026
The rule dates from the tape era; the modern reading is about independent failure, not exotic media:
- Laptop SSD + USB hard drive: different enough.
- Two partitions of the same drive: not two copies. One drive dies, both "copies" die.
- A NAS in the same house: counts as the second kind of storage, but not as off-site.
- Cloud object storage (S3, Backblaze B2): counts as both different storage and off-site — which is why a two-copy setup of "machine + cloud" is a defensible modern simplification of the rule.
The honest simplification
Perfect 3-2-1, maintained for years, beats nothing. But a 2-copy setup you'll actually keep running — original plus an automatic nightly backup, one of them off-site — beats a perfect design you abandon in a month. Start with the second copy. Add the third when the first is boring. Boring is the goal: backups should be the least interesting thing your computers do.