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Mastering the golden rule of 3-2-1 in data backup

by Advatek
March 11, 2024

A robust data backup strategy is a fundamental part of any IT manager’s plan and the 3-2-1 rule is the key to safely protecting data. What is the 3-2-1 rule for data backup

Quite simply this is:

  • 3 copies of your data
  • 2 different types of media
  • 1 off-site copy

So, let’s look at each of these elements in more detail and explore why this rule is so important…

3 copies of your data

When we say three copies of data, we mean your primary data set with at least two additional backups. Why? Well, obviously, two extra copies of data on stored two other devices means that the risk of complete data loss due to failure is extremely low.

For arguments sake, let’s say you keep your data on Device A and the backup is on Device B – if we assume that both devices have the same configuration or characteristics, and they have no common failure causes we can say that if Devices 1 and 2 have a failure rate of, say 1-in-100, then the probability of both devices failing at the same time is 1 in 10,000 (i.e. 1/100 x 1/100= 1 in 10,000).

Now, these are pretty good odds, and puts you in a good position in terms of being able to recover data.

Could both of these devices fail? Well not too likely, but it isn’t beyond the realms of possibility. However, when you throw that third device into the mix, then the probability of losing all your data becomes 1-in-1,000,000.

This really highlights why having more copies of your data greatly reduces the risk of data loss in the event of a catastrophic hardware failure. You should also bear in mind that by creating more than two copies of data, you can avoid a situation where the primary copy and its backup are stored in the same physical location.

2 different types of media

So, in the above scenario we’ve got our three copies of data and a one-in-a-million chance of losing everything… well, so far we’ve assumed that there would be no common failure causes across all the devices where copies are stored.

Of course, this requirement can’t be fulfilled if primary data and its backup are in the same place, and it isn’t that uncommon after one disk failure to see another disk failure from the same storage hardware at the same time.

This is why it’s good practice to keep data on at least two different storage types, for example on internal hard disks AND one other media (such as Tape), or on two internal disks in different storage locations.

1 offsite copy

What does it mean to have an off-site backup? Simply that the data is in different physical locations. It’s really not a good idea to keep your external storage device in the same room or building as your production storage. In the unfortunate event of a fire, you’d lose all of your data.

For larger companies, with more than one location, this may mean backing up to a tape and transporting to another office, or an off-site server backup. For SMEs, companies located at just one site, or schools and colleges, backing up to the cloud is a good solution.

Our approach to the 3-2-1 rule

As an IT managed service provider, we always recommend to all our clients that they follow the 3-2-1 rule for data backup.

Our own cloud-hosted backup solution, is easy, straightforward, and cost-effective solution which keeps your organisation running smoothly, protects from accidental deletion and malicious internal and cybersecurity threats and meets long-term retention and compliance requirements.