Actually --and for a month or two-- I don’t have physical access to the Drobo, so I can’t really answer with exact model number, but they are Western Digital 2.0 & 1.5 Tb Green EADS series.
The version of the firmware was the lastest one ( I updated 2 days ago ), the 1.3.5 I think… but I’m not known for my good memory so I might be wrong.
By the way, I think the WD Green series REALLY sucks bad. I had so much problem with this series in raid environnements (not only Drobo). The raid always drop them randomly. But if they are scanned with the WD utility, they are repported as good. I think WD try to push their new RAID Edition drive (RE), and volountary changed the WDTler setting to make unsuitable desktop-only drive: The Green/Blue/Black series.