fsync gives you durability and ordering, but often you only need ordering
fsync promises two things, durability and ordering, and I only need ordering. ext4 gives both or neither: every fsync commits the journal and flushes the disk cache. ZFS with sync=disabled gives ordering alone: transaction groups land in order, and a crash loses the last tens of seconds, not a database. My two HDDs are 2.7% busy instead of 13%, and a write takes 2 ms instead of 16.