[GrilledChips]

There's fuck all that ZFS can do if the drive lies about what has or hasn't been written yet, journal or no journal. USB devices are known to do this all the time.

If the drive lies and says that part of the journal has been written when it hasn't yet, and ZFS goes ahead and writes the next part of the journal, then when you unplug the drive and the first part of the journal goes away (which the 2nd depended on) you're hosed. There have to be places where ZFS blocks until something critical has definitely, absolutely, been written to disk.

At that point the only thing ZFS can do is try to unwind back to whatever it thinks is a consistent state, but this isn't 100% guaranteed. (it depends on what old data is still hanging around)