Big thanks for the quick reply Jared! I'm fearlessly forging ahead with the time consuming first task of cloning all 5 drives (one by one of course unless I get some other PCs out and fired up) with ddrescue before I do anything else with the faulty disk pack I'm hoping to recover. Since this likely is a drobo filesystem problem, I assume ddrescue will do nothing to improve the problem unless there is actually some kind of disk problem I'm unaware of and the copy process does some kind of repair by way of exposing missing data. Correct?
I'll have to google and see about UFSExplorer Pro. In general, I would be happy to at least get a full directory list so I can see what is on it. There are some old backups but we don't know what we are losing now if we take it out back and shoot it. (And that definitely sounds appealing.)
In general, I've always been nervous about Drobo but the last 4 years have been flawless with three drobos and they started out as just network backup targets and eventually started being used for some network file storage too. I am going to push for us to go back to that because I've always been nervous not having a full understanding of how they work like I do with traditional RAID. And now I'm being proven right which is never good. LOL
I'll endeavor to share whatever I discover as time moves forward. Right now, my plan is to get all 5 drives cloned and stick the cloned drives into the drobo 5N box and see what happens. Because.... why not?