The 3-2-1 backup rule

One of the timeless rules that can effectively address any failure scenario is called the 3-2-1 backup rule.

The 3-2-1 rule is very general and it works for all data types (individual and corporate) and all environment types (physical and virtual).

This approach helps to answer two important questions: how many backup files should I have and where should I store them?
In other words, the 3-2-1 backup rule means you should:


  1. Have at least three copies of your data.3-2-1 backup - Copy
    2. Store the copies on two different media.
    1. Keep one backup copy offsite.


Let’s consider these statements one by one in more details.


  1. Have at least three copies of data

By three copies, I mean that in addition to your primary data, you should also have at least two more backups. Why isn’t one backup enough? Imagine that you keep your original data on device #1 and its backup is on device #2. Both devices have the same characteristics, and their failures are statistically independent (they have no common failure causes). For example, if device #1 has a probability of failure that’s 1/100 (and the same is true for device #2), then the probability of failure of both devices at the same time is:
1/100 * 1/100 = 1/10,000
This means that if you have your primary data (on device #1) and two backups of it (on devices #2 and #3, correspondingly), and if all devices have the same characteristics and no common failure causes, then the probability of failure of all three devices at the same time will be:
1/100 * 1/100 * 1/100 = 1/1,000,000
This is why having more copies of your data means you will have less risk of losing data during a disaster. In short, if your data is important to you, be sure to make at least two backup copies.
Note: Another reason to create more than two copies of data is to avoid the situation when the primary copy and its backup are stored in the same physical location.


  1. Store the copies on two different media

In the section above, we assumed that there were no common failure causes for all of the devices where you store your data copies. Obviously, this requirement cannot be fulfilled if you save your primary data and its backup in the same place. (For example, disks from the same RAID aren’t statistically independent.) Moreover, it is not uncommon after one disk failure, to experience failure of another disk from the same storage around the same time.
That’s why the 3-2-1 rule suggests that you keep copies of your data on at least two different storage types, such as internal hard disk drives AND removable storage media (tapes, external hard drives, USB drives, SD-cards, CDs, DVDs, or even floppy disks), or on two internal hard disk drives in different storage locations.


  1. Keep one backup copy offsite

Physical separation between copies is important. It’s really not a good idea to keep your external storage device in the same room as your production storage. If there was a fire (knock on wood!), you would lose all of your data.
If you work for a company that’s an SMB with no remote or branch offices (ROBO), storing your backups to the cloud might also be an option. And tapes taken offsite are still popular among all company sizes.


Contact 5 Star Technology to implement a backup strategy, whether the backup is only for the data, for physical machines or for virtual machines we can help you keep the backup safe.

Only with 5 Star Technology you will receive weekly and monthly reports on the status of your devices (including the backup).