dead end?

I had a fully working Drobe 2nd Gen, and now I have some problems.
I recently updated my drobo with 2 new drives. I pulled out two 500mb drives and replaced them with two, 2 tb drives. I did this one at a time, and over a 16 hour wait for rebuild period for each drive. The swap was successfully rebuilt, and status was clear and the unit was functioning well. I cleaned up some files by deleting them from the drobo gen 2, and added many more files to the new capacity, and things went smoothly. The drive is currently 40% full, with 4 green lights showing. All was good, I was happy.
I wanted to back up my new macbook pro, so I attempted to use time machine to make the first of repetitive backups. This is where things went bad, as the backup failed to execute. I now can no longer have access to the drives through the finder on mac osx 10.10.1. Drobo dashboard does function, it reports that all of the drives and the device is healthy, ready to go. However, by using the disc utility in mac osx, the drive is unmountable. The utility calls for a repair after verifying it, and when I make that attempt, the utility states that the drive is not repairable, and that I should backup and try to save whatever data I can access. I have tried a different Imac, with USB instead of through the thunderbolt to firewire adapter with the macbook pro. Same results with that exist. I have also attempted to mount the drobo on a windows 8 machine from my work, no luck there either, nothing mounts at all.
I need to know what my next step is for accessing the data that is on the drive. Right now, there are four, 2 tb drives in the drobo 2, all green lights, and with 40% used for storage. Everything from the outside looks to be in good standing status. What is key to remember here is that I have no access to the actual files within the drives, as the drobo will not mount on OSX.
I have reached out to Drobo support, but alas, the so called world class service is of no assistance as the unit is way past warranty.

It appears as though I am caught by the short and furries here. I do have the option to upgrade, but my preference would be to have a unit that would be attached to my home router, as an ethernet connection. Migration from Gen 2 to the 5N seems unavailable by reading the migration chart. Because I use both PCs and Macs, my need is to have access from both systems, perhaps even migrating data from one to the other. Wouldn’t that be nice?

I have invested in the four, 2 TB drives, which is no joke, as well as having all of my data stuck on them.

Any advice moving forward would be great.

Try Disk Warrior, and see whether this helps.

If not, you would be needing to look into recovery.
Data Rescue is a popular choice.

I bought disc warrior and ran it. It untangled the mess, even though the Drobo dashboard said that the status was fine.
It rebuilt the drives, and now I am performing a backup to my macbook pro as I type. Looks to be half way done in its 5 hr process.

So, a shout out to Kelvin for the advice on Disc Warrior, its spendy but effective, and my data was worth recovering.

With 8tb worth of drive space in my drobo gen 2, I am hoping to squeak out a few more years of service.

I do wish that my 4 disc stack could be shifted over to a NAS Drobo unit without hassle. It appears as though that migration is impossible.

They have us all by the short and furries, don’t they?