The 3-2-1 rule says to keep three copies of your data, store them on two different types of storage, and keep one copy offsite. The original counts as one of the three.
Why each number matters
- Three copies mean that a single failure, or even two, still leaves you with your data.
- Two types of storage, such as a local disk and a cloud service, reduce the chance that one fault or defect affects every copy.
- One offsite copy protects against events that hit the whole building, like fire, flood or theft.
A small business example
Files live on the office server. A nightly backup goes to a separate disk in the office for quick restores, and a second backup goes to a cloud storage service. That is three copies, on two kinds of storage, with one offsite.
Modern additions
Many businesses now extend the rule by making one copy immutable or offline, so ransomware or a compromised account cannot delete it, and by confirming backups work through regular test restores.
Learn how this shapes our backup plans, or read whether backups protect against ransomware.