Ultra 4 dead disk & re-striping time

If you had removed disk while NAS was off and rebooted, yes it should have come online, but it will not restripe, you would have to insert another disk either cold or hot.
Now that you've inserted it I would not stop the process, unless it's not working. The disk test is quite short, certainly less than 30 minutes. If you leave it for 12 hours and its still testing then there is a problem.
Formatting and partitioning is not necessary and may create a problem for the readynas. The disk should not be partitioned .
The earlier events you described were unusual so it looks like you may end up having to recreate the entire volume.
If you have already aborted the process, you could try removing the partitions, testing using sea tools, then reinserting, but I am fearful this will not work.

tkelly - I am running 4.2.22 on three units, a new Pro 6 which was initialized on Sep 12 and the array moved intact from an NVX BE to the Pro 6. Then the array moved intact from an NVX Pioneer to the NVX BE. The first array is the primary with mapped shares, the second is my backup which is updated every night. Two 1TB Seagate drives were then installed in the NVX Pioneer and a factory default initiated. This was now my experimentation unit. The Pro 6 and the NVX Pioneer were upgraded on 9/21 and the NVX BE was upgraded on 10/3.

No signs of any disk problems yet. In the Pro 6 I have two 15 month old Hitachi HDS5C3030ALA630 3TB and two new WD30EFRX Red label drives. (One came with the Pro 6 and another purchased a little over week ago. In the NVX BE, I have two more of the Hitachi 3TB and two 27 month old Seagate ST31000528AS drives and two more of these Seagates in the NVX Pioneer. I would think that if I was going to have a failure, I would lose one of the Seagates. At one time I had 10, 8 in two NAS units and two spares. I have had to RMA two of the drives and have a third that has failed with increasing errors, while I debate whether or not to RMA it or just let it go. I also have one that has been removed from NAS service because of increasing errorsI have one more that has a climbing error count but is no longer in service.

I would suspect a disk problem rather than the OS. You never did state what the status of you backup is, so I would assume it is non-existent. I would work with technical support and see if you can get access to your volume back.

Thanks, papabear. I do have a backup and it looks like I will need to re-initialize the Ultra 4. I inserted new disk in bay 4 and 15 hours later the front panel still says 'Booting....Testing disk 4'. So I think it is toast. Since the file structure on backup disk is ext3, any suggestions on steps I should follow to get data back on NAS after I re-initialize? Will Ultra 4 try to reformat my external backup drive once I attach after loosing all old settings?

No it won't try to reformat your usb drive.
To restore the data, just create a backup job or jobs to pull the data off the usb disk.