1TB Volume gone missing on my 2nd Gen Drobo

About a week ago, my second Drobo (with four matching 1TB WD drives in it) has lost a volume. It previously had “Drobo2-1”, “Drobo2-2” and “Drobo2-3”. I now only have -2 and -3… And 1TB of stuff I need to access is on the -1 volume which isn’t showing up.

I have this hooked to an Intel iMac via FireWire. Power cycling computer and Drobo has not helped. I was at 1.3.4 and even updated it to 1.3.5 and still nothing.

In Disk Utility I do see the volume, unmounted, and I can verify it (“The volume Drobo2-1 appears to be OK.”) but cannot mount it. It reports “The disk ‘Drobo2-1’ could not be mounted. / Try running First Aid on the disk then retry mounting.”

Any clues?

(I submitted this as a support inquiry on the Drobo main site last week but have yet to hear back…)

Run repair disk from Disk Utility on that volume.
Actually run it on all your volumes.

Good timing. I had just re-edited my original posting to include the fact that I tried that.

Drobo techs had me downgrade my dashboard because of issues it has related to volumes, and I am going to try upgrading it again to see if that makes a difference.[hr]
Update: All volumes (5 on my first Drobo, 3 on the second) verify OK to Mac Disk Utility, though Drobo2-1 will not mount.

Follow-up: After playing with this awhile, I finally ran DiskWarrior on the volume and for the moment it appears back.

(edited: corrected typo)