they need at least perform fdatasync before replying to a client, imho. so I do not think it's every x seconds. I am not deeply familiar with scylla so maybe I am mistaken.

I think you're wrong. It does that every x seconds. The disk writing is async and it's meant that you protect data-loss by keeping replicas in different availability zones.

interesting. i still need to learn a lot about how other systems provide durability guarantees. Based on what you are saying, Scylla guarantees H/A instead of full durability. I was thinking about WAL (AOF) for dragonfly and I kinda thought to start with "fdatasync once in every X seconds", but dragonfly is not a database. I would expect stronger guarantees from databases. Maybe it's inpractical to expect this in cloud environments...

It wouldn't have the performance that it has. Cassandra does the same. YugabyteDB does the same https://docs.yugabyte.com/preview/reference/configuration/yb....

> I would expect stronger guarantees from databases.

You can configure it and get lower performance.

> Maybe it's inpractical to expect this in cloud environments...

For benchmarks they use raid0 on local disks(not EBS) in aws vps.