3-2-1 rule

Last week I wrote about the OpenVPN instance I set up at home so I could access easily and with relative security my NAS without opening it to the outside.

The reason for having a NAS is to cover partially the 3-2-1 principle for backups, so the chances of losing my data is as low as I can (it could probably be lower just paying Google or Dropbox, but I would rather keep my data myself).

The 3-2-1 principle is as follows:

3. Keep at least three copies of your data

Three copies reduces the chances of all copies failing at the same time considerably, but also gives the chance to apply a majority rule when some data happens to be corrupt.

2. In two different different storage types

Failures on hard drives from the same batch are strongly correlated. This means, they have the same life expectancy. Therefore, when once fails, the other is very likely within its “danger zone” too. Additionally, the failure of one drive will put extra load on the remaining survivor, which is now going to move faster towards its sad end. Chances of a second drive dying shortly afterwards a failure increases a lot.

This is not theoretical, this happens to the NAS of a friend.

If you mix different media (Blueray and disk), different brands, or, at the very least, different batches, this risk is greatly reduced.

1. One off-site

If the three copies are on the same “site” (home), and there is a fire, or a flood, or a burglary, then all copies are lost.

One copy should be kept somewhere else: relative or friend’s place, at work, etc.

And the twist

I print one album per year with a photo collection. That gives an extra copy, in a non digital media, so chances are I will have something in 20 years.