RAID rebuild issue

Hi guys,

I have 2x2TB seagate disks in a thermaltake USB 3.0 dock. I setup a RAID 1 (mirrored raid set) so that everything is written on both disks at all times. I'm a photographer so this seemed like a good way to backup my edited photos.

Anyway, RAID failed for some reason, and the rebuild button from disk utility doesn't help since it ejects the disk with an error after a couple of hours. "The disc was not ejected properly" error (as if I had pulled it out in the middle of something).

I don't know why this happened, and I'm not sure what to do? I have all my data, but I need this RAID to work.

Tnx!