The 3-2-1 Backup Rule
The simplest rule that saves businesses
The 3-2-1 rule is the most widely accepted backup strategy. It’s simple, effective, and technology-agnostic:
- 3 copies of your data
- 2 different storage media
- 1 copy offsite
Why three copies?
One copy is no copy. If your only backup sits on the same server as your data, a single event (fire, ransomware, hardware failure) destroys both.
Two copies is better, but still risky. If both copies are on the same media type (e.g., two hard drives), a manufacturing defect or firmware bug could affect both.
Three copies makes simultaneous loss statistically improbable. You’d need three independent failures at the same time.
Why two media types?
Different storage technologies fail differently:
| Media | Typical failure mode |
|---|---|
| HDD | Mechanical wear, head crash |
| SSD | Write endurance, controller failure |
| Tape | Degradation, drive incompatibility |
| Cloud | Provider outage, account compromise |
| NAS | RAID controller failure, ransomware |
Using two different media types means a single failure mode can’t wipe all your copies. Common combinations:
- Disk + Tape — the classic enterprise approach
- Disk + Cloud — modern hybrid strategy
- NAS + External Drive — small business approach
Why one offsite?
Local disasters don’t care about your backup strategy. Fire, flood, theft, or a power surge can destroy everything in one location. One copy must be physically separated:
- Remote datacenter — another building, another city
- Cloud storage — geographically distributed by design
- Tape vaulting — physical tapes stored offsite
The 3-2-1 rule with Bareos
Bareos supports all of these scenarios natively:
- Multiple pools for different copy levels (Primary, Copy, Archive)
- Copy jobs that duplicate backups to a second storage
- Cloud storage integration for offsite copies
- Tape support for air-gapped backups
Onesimus will visualize this in the Pro edition — see all your copies, pools, and storage locations in one view. Community already lets you manage the jobs and schedules that make 3-2-1 work.
Beyond 3-2-1: The 3-2-1-1-0 rule
Modern best practices extend the rule:
- 3-2-1 plus 1 air-gapped or immutable copy
- 0 errors — verify every backup with automated restore tests
The extra “1” protects against ransomware that specifically targets backup systems. An air-gapped tape or an immutable cloud snapshot can’t be encrypted by malware.
Learn about backup levels: Full, Incremental, Differential →