Comment by solatic

> Even if you RAID them, there's not a good way to move that VM to another host if there's a RAM or CPU or other hardware issue on that host.

This is the critical point. All hardware fails eventually. The CPU and RAM are, in a real sense, also ephemeral. The only relevant question is what the risk tolerance of the use-case is. If restoring from async backup is sufficient, then embrace ephemerality and keep backups. If you need round-the-clock availability, pick an architecture that lets you fall over gracefully to another machine, and embrace the ephemerality when you inevitably need to do so.