Jeff, that makes sense then.  I had it set to results to grid, so I did get the million rows plus those messages.  Well, on one of the 2 SSMS...

That'd be my next guess.  I would think that SQL would need to do some form of sanity check to make sure that the data pages are all properly in...

You say you have 18,000 data files.  are those all on different disks?  If not, you will not really get a performance benefit and I can see that causing a...

I might have an idea - how many VLF's do you have?
DBCC LogInfo(<database name>)

If you have a crazy high number of VLF's, that will greatly...

Did you look in the event log?  I am willing to bet that that is exactly what it shows in the event log.  I've sen those types of messages in...

I've not done much (ie anything) with windows failover clustering,but that dependencies list doesn't look like it lists cluster disk 5 as being included in the failover.

As a...

9 TB of data is a lot of data to restore, so it doesn't surprise me it takes a while especially on a system with that low of memory.

Right.  About the CHECKDB thing.  that threw me off.  But you have not run checkdb in quite some time, no?   2017-01-19 appears to be the last time it was...

If I understand the logic correctly, I think this is more what you want for your loop:
WHILE EXISTS(SELECT 1
             ...