Hi n_u, PlanetScale engineer here, I'm going to just address just the point about durability via replication. I can't speak to what you've seen with other distributed systems, but, at PlanetScale, we don't do replication instead of writing to disk, we do replication in addition to writing to disk. Best of both worlds.

Good point, Max. I glossed over the "rather than" bit. We do, as you say, write to disks all over the place.

Even writing to one disk, though, isn't good enough. So we write to three and wait until two have acknowledged before we acknowledge that write to the client.