You say that to someone that has personally brought up 4 16-drive 4RU units on a Friday with brand new drives and then left over the weekend to complete the striping and an initial warm up process of writing/deleting files to the array. When I arrive on Monday, multiple drives in each enclosure had failed which meant not data recovery would have been possible. Luckily, it was during the warm up and not 2 weeks later after being active. After contacting our vendor, all drives were replaced not just those that failed. Later discovered that it was a manufacturer issue, and multiple other clients of our vendor had similar experiences.
While statistically it might equate to "unlikely" as you state, the fact it did happen, I now have that experience that is not forgotten. Never bring a large storage pool into PROD immediately after the array finishes striping. Put it under load for a period of time first. The question remains on how long that period is though which is probably answered with "how paranoid are you"
> Luckily, it was during the warm up and not 2 weeks later after being active.
While there's always luck involved, dying during warmup and not two weeks later is the expected experience for drives that defective.
So what happened to you wasn't that you made a backup and then it failed so fast you couldn't use it. It's relevant to what I was saying is unlikely, but it's not an example of it.
Plus at zero weeks or even two weeks you have the previous backup system around. If you have a big simultaneous failure 6 months out, that's a scary situation, but that's much rarer.