I've recently been looking up RAID 1 setups myself.
I have room for 4 3.5 drives on the inside of my case and 2 quick slots.
Currently I only have a 320gb solid state for important programs (W8OS, Adobe CS6, Microsoft University 2010, and extra space for temporary video storage for editing.)
And a 1TB WD Black for everything else including RAW storage (sounded like the most reliable drive)
But that 1TB drive is running out of space, so I'm thinking of getting another 1TB WD Black to run RAID 1 for RAW files only, and a 4 TB WD Black for everything else.
Of course Backing up with Lightroom is Probably a lot cheaper than buying a RAID controller and additional drive, The only advantage to a RAID 1 is you don't have to compress and backup files.

Good luck with your recovery!

I'm backing up my 520GB music library, and I thought *I* had problems.

A professional photographer I follow on Youtube always recommends the Drobo brand external storage systems because it uses one of the RAID systems for data redundancy and the drives are hot-swappable in case one goes out. In that case it reconstructs the data onto the new hard drive, but everything is still accessible and usable while it's working.

Drobo has another advantage: Unlike RAID, the drives don't have to be identical - they don't even have to be of the same capacity. As your library grows and HDs become bigger and less expensive per TB, you can simply pull out the smallest drive and stick in a bigger one from time to time, thereby enabling relatively painless continuing growth.