Comment by ryao

ZFS is not journaled. CoW eliminates the need for anything like a journal with the exception of synchronous IO, where an intent log is used that can be replayed after a power loss event.

In any case, ZFS should be fine as long as REQ_PREFLUSH is working properly. You can read a little about that here:

https://github.com/openzfs/zfs/blob/453c63e9b74cea42d45e0bd3...

https://elixir.bootlin.com/linux/v4.18/source/include/linux/...