[anotherhue]

I suggest playing with the ZFS tunings to add a write throttle. My hunch is your disk's buffer is filling and then blocking.

[tripleo1]

I think that there was an electrical problem (mismatched chargers on a laptop) in the first instance of mine.

Then there's encrypted datasets being very slow, especially when copying between two pools.

Then there's having two pools on the same disk corrupting each other. Though in this case the data might have been recoverable using some recovery tool (like a "modified zdb").

Also, I read on some website somewhere (maybe zfsonlinux.org) that USB devices probably shouldn't be used with ZFS.

Honestly I "wish" some bunch of crazy filesystem people would just clean room ZFS...

[quectophoton]

That sounds like a good idea, you just gave me new keywords to search for my next attempt.

Thanks!