zfs mirror: 1 disk lost, corrupted other disk. crashes zfs tools and panics system

[Edward Sutton]

  Wanted to report from a state I could describe without confusion of steps I had taken. Restored DD copy and ran `zpool import -fFX zroot` from the same -current disk mentioned earlier and this time it did roll back a few minutes and gave access to the corrupt filesystems. I must have touched it more with an older copy every time though I thought that was not the first time I started with -current. -X still is not defined in the manpage but is referenced a lot online.
  I still have the disk copy that can be restored in the corrupt form if anyone is interested in fixing issues such as scrubbing without the v28 rollback taking place. The scrub was when it got stuck in a panic on import because the scrub would resume and would cause a panic in doing so.
  Current was prone to occasional random crashes on my system so it took a while to copy off the data in a successful run, though that may be my hardware (which seems most stable after being up and running for a few hours under full cpu load such as boinc).