3
Keep 3 copies of your data
Original, plus two backups. One copy lives on your main system, one on a separate device or network and one off-site.
- Your working files (production data)
- A local backup on a NAS, external drive or separate server
- An off-site copy in the cloud or at another physical location
2
Use 2 different storage types
Don't put all your eggs in one basket. Mix local and cloud, or use different hardware so a single failure can't take everything.
- NAS or external drive (local / on-premise)
- Cloud backup service (Azure Blob, AWS S3, Backblaze, etc.)
- Different media reduces risk of correlated failure
If your office floods, burns or gets hit by ransomware that spreads across the network, your cloud copy is untouched and ready to restore.
- Encrypted cloud backup (always encrypted in transit and at rest)
- Physical drive stored off-site for critical data
- Geographically separate from your primary location
The even better version: 3-2-1-1-0
A modern twist adds two more rules. One copy should be immutable or air-gapped (cannot be modified or deleted, not even by ransomware). And your restore process should achieve a 0-error rate in testing, meaning you've actually verified the backup works end to end.