Drive failure(s) in linux mdadm raid array. Help!

It looks like my system is suffering from some sort of catastrophic failure, and I'm panicking at the moment, not sure what to do. I had a 3 drive raid 10 array. I noticed this morning that I was having trouble accessing the array (all my photos are on there). I checked mdadm and it said that one drive was dropped from the array (drive 2). I think this may have been because the computer was shutdown accidentally (there was a blackout), and the drive was kicked as a result. I tried adding the drive back, and that worked. Then I checked the progress of the rebuild with mdstat, and it is rebuilding at 10 kb/s. Yes. It would take years to rebuild a 3 TB drive at that speed. I check dmseg, and I was getting a bunch of I/O errors for drive 3. It seems that drive 3 has some kind of hardware failure. I checked the drive's health with the disks tool (I think it's from gnome, gnome-disk-tool or something), and it had almost 6000 bad sectors, but apart from that it said it was OK. So now I'm panicking, thinking that the drive 2 was actually still good and now when I readded it, it's resynching, probably destroying the good data it has. I then tried turning off the computer (I read it was save to do so even when mdstat is resyncing). Unfortunately, the shut-off is not working. Pressing "ESC" showed me the terminal and it's displaying a bunch of "print_req_error: I/O error, dev sdd, sector ...." type errors. I don't know what to do. Just wait? It's been going on for 30 minutes like this. Any advice?