Photographer Peter Krogh popularized the 3-2-1 data backup rule
Peter Krogh introduced a specific framework for storing digital files in his 2009 book.
The three copies requirement
The rule states that users must maintain three total copies of their data. These copies ensure safety if one storage device fails or is lost.
Two different media types
Those three copies should be stored on two distinct types of media. Recent interpretations often define these as two different physical devices rather than just file formats.
One offsite location needed
At least one of the required copies must be kept at an offsite location. This arrangement protects data from local disasters that could destroy all on-premise storage simultaneously.
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