[nh2]

> you can configure the kernel to ignore that, and by default it does.

> The modern linux kernel doesn't actually write to disk when fsync is called.

This is false.

Almost all open source databases' durability guarantees are based upon fsync (including SQLite, Postgres, MySQL, and so on). fsync will result in the corresponding underlying storage flush commands. You configure Linux to ignore fsync, but this is is not the default, on any Linux distribution I'm aware of. It would not make any sense.