For readers in a hurry, here’s a summary of the most important facts. In the 3-2-1 backup rule, each number refers to a feature of the backup process:
3: Signifies the number of data versions to save – one original and two copies.
2: Stands for two types of media to store your data on, for example, an external hard drive and a cloud account.
1: States that one copy must be kept “offsite” for disaster recovery, that is, one data copy will be stored on a medium that is not kept at the user’s home or a company’s office.