Is that entirely true? If you have a replication protocol like Viewstamped Replication you have the option to make a trade off for how many machines you the will fail concurrently vs forcing an fsync.

I think I'm a bit of an outlier here on that k never really understood why durability requires fsync. It doesn't help you if the storage dies. If durable storage is important to you, then isn't the only solution to synchronously replicate to a quorum of machines at which point an fsync isn't that relevant? What am I missing?