Within this rule you should have at least 3 backup copies in at leat 2 different storage destinations, one of which is offsite. This backup rule esures that you can restore your data in diferent disaster scenarios, for example, if there is an infrastructure outage.

Here is apost where you can find out more about the 3-2-1 backup rule and its morden alternatives - the 4-3-2 and 3-2-1-1 backup strategies: https://xopero.com/blog/en/the-evolution-of-data-backup-is-t...