I have progressed a little further with this problem.
I thought that if a drive failed, there would be no activity on the drive. You would see this in the WRKDSKSTS command where the stats on the failed drive should all be zero. They were not.
I have restarted my machine into manual mode and went to DST and work with disk units. Options, 4, then 2, then option 12.
The system identified the failed drive and I was able to rebuild the drive. The system recovered everything on the unit. Its up and running without problems… so far.
I guess the lesson learned is they do not always fail completely. I will get a replacement unit to keep on hand.