DiskWarrior Error (-36 2747) "hardware failure" unless you wait for hours: solution

When I connect the DROBO and try to run DiskWarrior, I get an error -36 "hardware failure".  

I can hear the DROBO doing "stuff".

If I wait several hours until the DROBO is quiet, then DiskWarrior doesn't get the error, and I can try to recover it.

Scratched my head over this for a while, so figured I would post the solution in case anyone has the same problem.

All the forum posts are about dead disks.  

My disk isn't dead, it just has a sick filesystem, as proven by the fact that if I wait long enough, DiskWarrior can try to do something with it.

The disk activity was a clue.  

I suspected that TimeMachine or something else on the mac is trying to fsck the file system in preparation for mounting.  Unfortunately that takes HOURS on this large volume full of time machine backups.

So opened Terminal and typed: ps -ef | grep fsck_hfs and there was the culprit:

To kill it, type kill followed by the second number from the left, in this case: kill 67332

The disk activity stops, and you can then run DiskWarrior.