The 3-2-1 backup rule: how not to lose your data

Published 2026-11-03 · 5 min read · By the Alian Digital team

A disk fails, a laptop is stolen, a virus encrypts your files. The only reliable protection is backups you have tested.

The 3-2-1 rule

• 3 copies of the data: the original and two more.
• 2 different types of media: for example, a computer and a network storage.
• 1 copy in another place: the cloud or another office.

What it looks like in practice

For a small office: files on computers, an automatic copy to a NAS in the server cabinet and an encrypted copy in the cloud. For a home: a laptop, an external disk and the cloud for photos and documents.

Why one copy on the next disk is not enough

Ransomware also encrypts connected disks, and a fire or theft takes everything from one place. So you need a copy the virus cannot reach: disconnected, in a cloud with version history or with deletion protection.

What to back up

• Documents and accounting files.
• Mail and calendars, if they are not in a cloud with backups.
• Databases and website files.
• Equipment settings: routers, switches, cameras.
• Photos and important files from phones.

Automation and checking

• Backups must run by themselves, on a schedule.
• Encrypt copies and keep the keys separately.
• Set up failure alerts.
• Every few months restore one file to make sure the backup works.