The 3-2-1 Backup Rule: Three Copies, Two Media, One Offsite
Engadget explains the 3-2-1 backup rule: keep three copies of important data on two types of media, with one copy kept offsite, so that a failed drive, a house fire or a ransomware attack does not destroy the only version of your files.
The framework was first popularized by photographer Peter Krogh in his 2009 book, "The DAM Book: Digital Asset Management for Photographers," according to Engadget. At its baseline, the rule calls for three copies of a given set of files, stored on two kinds of media — often interpreted today as two different devices — with one of those copies held somewhere other than the user's home.
Engadget's explanation sets out why each part of the formula matters. A single copy on one SSD leaves its owner with nothing if that drive dies. Making copies to several drives in the same location still leaves everything exposed to a flood, a house fire or a burglary. Keeping one copy elsewhere adds a layer of protection, and the offsite copy should ideally sit far enough away that a disaster affecting the home would not also affect the place where that other copy is stored.
The rule has shifted as technology and the threats against data have changed. Few users burn CDs today, and worries about media becoming obsolete have eased, Engadget reported, pointing to discussions on sites such as Reddit where people describe how they adapt the 3-2-1 approach to their own needs and budgets. The requirements of an individual are not the same as those of a multinational corporation.
In practice, that could mean keeping files on a laptop, an external hard drive and a private cloud server. Services such as iCloud or Google Cloud can serve as one of the copies, though Engadget cautions that, depending on the service and its syncing settings, deleting a file from a computer may also delete it from the cloud. Other services offer automatic full backups of devices, with various storage limits and pricing tiers.
Networked storage brings its own exposure: an offsite copy can still be vulnerable to a ransomware attack if the device holding it is connected to a network, Engadget said. The publication describes the rule as a relatively straightforward way to think about preserving important files.