The 3-2-1 backup rule, simply explained
The 3-2-1 rule is the best known rule of thumb for backups. It sounds technical, but it is quickly explained and easy to follow on a Mac.
The rule
- 3 copies of your data: the original on your Mac and two backups.
- 2 different kinds of storage: for example an external disk and a NAS or cloud storage. If one kind fails, the other remains.
- 1 copy offsite: in the cloud or at a friend's place. Only distance helps against burglary, fire and water.
Why two backups?
A single backup often fails exactly when you need it: the disk died, it was next to the stolen laptop, or the backup had not run for weeks without anyone noticing. Two independent backups make it very unlikely that both are missing at the same time.
What it looks like on a Mac
- Time Machine or another tool to an external disk at your desk, hourly.
- A second backup to a NAS or cloud storage like Cloudflare R2 or Backblaze B2, daily, encrypted.
- Once a month, check that files can really be restored from both.
The forgotten part: checking
The rule says nothing about whether the backups work. Restore a few files regularly and compare them with the originals. Only then do you know your three copies really are three.
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