Disk failure happens quite frequently for me at scale, but so do other things like RAM going bad or network cards dying or entire mainboards just acting weird o

Disk failure happens quite frequently for me at scale, but so do other things like RAM going bad or network cards dying or entire mainboards just acting weird or top-of-rack switches silently dropping packets because of memory corruption (all of these have happened to machines I'm responsible for in the last six months). Again I think this is a matter of scale. If you've got enough machines that disk failure is a concern, you can also run a 9-node etcd cluster and have a big enough pager rotation that keeping 5 of them up 99.999% if not 100% of the time isn't a challenge. If you have less than a rack of machines and you're not at the point where you're worried about having a SPOF in your network switches or power supplies, running etcd a bunch of overhead for a problem you don't have and you are genuinely better served by a robust non-distributed system whose availability is the availability of your hardware.