RAID is not very reliable. Here is an example that I tried the other day in MD RAID 1. I made a 2-disk array, zeroed it, wrote a sector of garbage at 1MB into one disk directly, cleared caches, ran a scrub and did not see any warning about the inconsistency. It relies on the drive firmware to verify the low level formatting parity, so things like misdirected writes (which my writing garbage was meant to simulate) go undetected. There are plenty of other problems too, but that is just one example. Anyway, at scale, you can count on RAID to be unreliable. If you want something reliable, use ZFS.