Which information technology rule requires three copies of data, two copies on two different media, and one copy off-site?

According to the 3-2-1 backup rule, you need three copies of your data, on two different media, and one copy off-site. Grandfather-father-son is a rotation scheme for backup media. There is no widely accepted rule known as the on-site/off-site backup rule. The accounting rule of 78 is utilized to determine interest payments.