What is the 3-2-1 backup rule?
It is a simple rule for surviving the loss of any one thing: keep three copies of your data, on two different types of storage, with one copy off-site. The original plus two backups, for example one on a local backup appliance and one in a separate cloud or at another location, means that a fire, a failed disk array or a stolen server does not take everything. Because ransomware attackers now look for backups and try to delete them, many guides extend the rule to 3-2-1-1-0: one copy that is offline or immutable, so that it cannot be changed or deleted even with administrator rights, and zero errors when the backups are verified and test-restored. For a small company, a practical version is a local backup for fast restores, an immutable cloud copy under separate credentials, and a regular, documented restore test.