What is the 3-2-1 Backup Rule — and Are You Actually Following It?
Most people think they have a backup. Most people don’t have a good enough backup.
A single backup copy on an external drive isn’t enough. If your house floods, gets broken into, or a ransomware attack encrypts everything on your network — that backup goes with everything else.
The 3-2-1 rule is the industry standard for doing backup properly. It’s simple, and it works.
What is the 3-2-1 Backup Rule?
3 — Keep at least 3 copies of your data 2 — Store copies on at least 2 different types of media 1 — Keep at least 1 copy offsite
That’s it. Three numbers, three principles.
Breaking It Down
3 Copies
Your original data counts as copy one. You need at least two more backups. Why three? Because two copies isn’t enough — if both copies are affected by the same event (ransomware, fire, hardware failure), you have nothing.
Three copies means you need multiple simultaneous failures to lose everything. Statistically, that’s very unlikely.
2 Different Media Types
Don’t put all your backups on the same type of storage. If you back up to two external hard drives and that model has a manufacturing defect, both could fail. “Different media” means a mix of:
- Internal SSD + external hard drive
- External hard drive + cloud storage
- NAS device + cloud storage
Cloud and local storage together is the most practical combination for most people.
1 Offsite Copy
This is the one most people skip — and it’s the most important. An offsite copy protects against physical disasters: fire, flood, theft, or anything else that could destroy everything in one location.
“Offsite” can mean:
- Cloud backup (easiest and most reliable)
- An external drive kept at a different location (parent’s house, office)
- A NAS device at a second location
Cloud backup is by far the most practical offsite solution for most people.
What Does a Good 3-2-1 Setup Look Like?
For Home Mac Users
| Copy | What | Where |
|---|---|---|
| Copy 1 | Original data | Mac internal drive |
| Copy 2 | Time Machine backup | External drive at home |
| Copy 3 | Cloud backup | Backblaze Personal |
Cost: ~£7/month for Backblaze. Time Machine is free if you have an external drive.
For Home Windows Users
| Copy | What | Where |
|---|---|---|
| Copy 1 | Original data | PC internal drive |
| Copy 2 | Windows Backup | External drive at home |
| Copy 3 | Cloud backup | Backblaze Personal |
Cost: ~£7/month for Backblaze.
For Small Businesses
| Copy | What | Where |
|---|---|---|
| Copy 1 | Original data | Server/workstations |
| Copy 2 | Local backup | NAS or backup server on-site |
| Copy 3 | Cloud backup | Acronis Cyber Protect / Backblaze Business |
Cost: Varies by size, typically £10–20/device/month for a complete solution.
Common Backup Mistakes
“I have an external drive so I’m fine” One local copy is not enough. That drive could fail, get stolen, or be destroyed in the same event as your original data.
“It’s all in Dropbox/OneDrive/Google Drive” Cloud sync is not a backup. If you accidentally delete a file and the deletion syncs across all devices before you notice, it’s gone from your sync service too. Proper backup has versioning and retention.
“I back up once a week” How much work can you afford to lose? Weekly backup means potentially losing a week of work in a failure. For critical data, daily or continuous backup is better.
“My Mac is backed up to Time Machine” Time Machine is excellent — but it’s a local backup only. Add Backblaze or another cloud backup for offsite protection.
“Microsoft 365 backs up my emails” Microsoft 365 has retention policies but they are not a backup. If data is permanently deleted or corrupted, Microsoft may not be able to recover it. You need a dedicated Microsoft 365 backup solution.
The 3-2-1-1-0 Rule
Some IT professionals now use an extended version of the rule:
3 copies 2 different media 1 offsite 1 offline (air-gapped, not connected to any network — protects against ransomware) 0 errors (regularly verify your backups actually work)
The 0 errors part is often overlooked — a backup you’ve never tested is a backup you can’t trust. Restore a test file occasionally to confirm your backup is actually working.
Getting Started
If you’re not following the 3-2-1 rule yet, start here:
Home users: Set up Time Machine (Mac) or Windows Backup to an external drive, then add Backblaze Personal for cloud backup. Done in an hour, costs ~£7/month.
Small businesses: Talk to your IT provider about a proper backup strategy. If you don’t have one, Acronis Cyber Protect is a strong starting point for businesses needing a managed solution.
Ready to sort your backup? See our guide to the best backup software for home and business.