Why backups fail — and the 3-2-1-1-0 rule
How businesses actually lose data
- Ransomware encrypts the server and every backup it can reach.
- Human error: a deleted folder noticed three weeks later, after the backup kept only 14 days.
- Hardware failure: a RAID controller dies and takes the array with it.
- Site loss: fire, flood or theft takes the server and the USB drive sitting next to it.
- Silent failure: the backup job has been failing for months and nobody read the alert.
The 3-2-1-1-0 rule
| Number | Meaning |
|---|---|
| 3 | Three copies of your data (production plus two backups) |
| 2 | On two different types of media or systems |
| 1 | One copy off-site |
| 1 | One copy offline or immutable (cannot be changed or deleted, even by an admin) |
| 0 | Zero errors — verified by restore testing |
RAID, sync and snapshots are not backups
- RAID survives a disk failure but faithfully mirrors deletions and encryption.
- Sync tools (OneDrive, Dropbox) replicate mistakes everywhere within seconds.
- Snapshots on the same storage disappear with that storage.
They are useful layers — but you still need independent, versioned, off-site copies.
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