Hmm. This is a tough one. At one point in time you had more than one drive in the disk pack as Drobo wouldn’t let you create a disk pack consisting of only one disk.
Since you’re on a completely different Drobo setup (different chassis, different hard drive) and different computer, the source of corruption can be limited to extremely bad luck, misbehaving software, or unsafe removal (not using Safely Remove or gracefully shutting down the OS) practices.
It makes me shudder when people just yank out USB devices… I’ve completely scrambled data on USB keys and USB hard drives that way. Just because the interface supports hot unplug doesn’t mean the device accessing it was expecting it to be unplugged. Not saying that’s what’s happened here - just making a general comment.
Dashboard doesn’t handle the filesystem - it only peeks at how much data is being used. Dashboard doesn’t see a filesystem, but the Drobo has a drive and a configured disk pack, thus it doesn’t detect any problems.
Unfortunately I’m not sure what advise to give you at this point… by reducing the Drobo disk pack to a single drive, any chance of it relocating data to another drive in the event the drive is going bad has been eliminated.
Perhaps someone else will have an idea.