Comment by gruez

>part of a write cache's job is reordering writes to be more efficient which means ordering is not generally preserved.

you can use some sort of WAL mechanism to ensure that the the parallel writes appear as if ordering was preserved. that will allow you to lie and ignore fsyncs, but still ensure consistency in case of a crash.

>But then again, if they're willing to accept and confirm flush commands without flushing, I wouldn't expect them to actually follow ordering constraints.

it depends on which type of liar they think you are. if they're the "don't care, disable all safeguards type", then yes they're probably ignoring ordering as well. However, it's also possible they're the methodical liar, figuring out what they can get away with. As I mentioned in another comment in this thread, as long as ordering is preserved the lie wouldn't be noticed in typical use cases (ie. not using it for some sort of prod db, and not using it as part of a multi-drive array). power losses are relatively common, and a drive that totally corrupts the filesystem on it will get noticed much more quickly than a drive that merely loses the last few seconds of writes.