In backup terminology, people sometimes refer to the 3-2-1 rule to secure data and guarantee recovery in case of urgency or end-user request. The 3-2-1 backup rule means:
- Have at least three copies of your data.
- Stored on two different media.
- One copy offsite in a secure location.
Three copies not including the primary data. Maybe this is a bit too much depending on your backup strategy. Most of the times I try to keep two copies of my data on two different media (disk storage and tape storage). Both of them are kept by using a predefined retention scheme and send-out to an offsite location by using a predefined retention scheme.
Anyhow, this rule is a guideline and should be used according your own convenience. A more important rule is to ensure the quality of your backup by planning some periodic restore tests. Backup wouldn’t be backup if we simply belief the green dot indicating successfulness. Additionally these restore tests gives us the ability to create restore procedures which will help when a full system recovery is required.