I had a similar experience with my 3TB backup drive although in fairness it was my fault. I accidently wiped my drive by being stupid LOL. Anyway I tried Recuva and got nothing of any use back. I eventually bought a program called Seagate Recovery and that did recover around 90% of the content. Note that fact that I bought it. The freebies did nothing. Seagate Recovery was expensive, well I thought so, but it did the job. I now keep by backups on three different drives none of which is connected to my computer when I am not using them. I would go with a RAID array but that is not cheap but I do keep looking at that option. Oh yeah that Seagate recovery program did take three days to recover my data. I just left it running whilst it wasn't telling me anything was wrong. It did, eventually, finish so if do get it be patient. Also I give no guarantees that it will work all I am saying is that it worked for me.
