Use dissimilar systems for backup

The good rule to follow in any redundant system, and in backup specifically, is:

Primary and backup systems should be dissimilar.

This rule applies to both hardware and software. If your primary storage is FreeNAS with ZFS, use Windows Server for your backup storage, and vice versa. If you have a RAID1 with two disks, use disks with similar performance but from two different manufacturers.

If you use two identical systems for redundancy, you are setting yourself up for one or another common mode failure. Eventually, something like this happens:

OMG. I bought two identical systems back in April/May. One is my primary on-site backup storage, the other is my off-site storage. A couple hours ago, the on-site unit crashed and won't reboot. Now the second unit has crashed! It fails to boot with the same error message. What?


Obviously, there are some practical limits to dissimilarity. If you have a 48-disk shelf, it is not wise to populate it with different models of drives from different manufacturers. Performance implications aside, there are not enough distinct drive models out there. The more practical solution is to have a primary system set up with drives of one model, and even possibly from the same manufacturing batch, and a backup system set up with a set of drives from a different vendor. So, if one set of drives turns out to have a firmware issue, a la Seagate 7200.11, the other set of drives is unaffected.

Created Sunday, September 1, 2019