[Psychlist]

Also: different NAS hosts, RAID cards, etc. Those have correlated failure modes too.

My personal backup strategy of buying a different backup drive every time seems wiser the more I learn.

At work we have two different NAS setups, each full of a different brand of near-identical drives. But what we have been doing is buying a few new drives every quarter and rotating them in to the NAS boxes. So they're all WD 6TB Black or whatever, but of 12 drives we now have 4 original ones, then a pair 3 months newer than that, a pair 6 months newer and so on. The "old" drives go into random stuff round the office because we employ engineers and they seem to all like to have their own little 2-4 drive NAS boxes for "important stuff" (which is in many ways fine, we just have to regularly coach them on making sure the stuff they're actually working on is on our NAS where it gets backed up. We host a gitlab instance, for example, so their code and project docs are in that).