Mac – 3 Terabyte hard drives in Mac Pro Mid 2010

You're not the first person to have problems with this drive in a Mac - see http://www.mac-forums.com/forums/apple-notebooks/217444-macbook-pro-hard-drive-replacement-wont-format.html

It's possible there is a compatibility issue, as you seem to be doing all the right things (and it is connected properly otherwise you wouldn't see it in Disk Utility at all).

The damaged hard drive bracket would not be the cause of the error above.

Try a non-AV drive (one designed for notebooks rather then surveillance/home theatre use) and see if that makes a difference.

Well you already have a pretty optimal setup. Having the two disks in RAID-0 as your boot drive gives you the greatest possible performance. Just be sure to keep a good backup, since if either disk fails you lose the whole array. Superduper! is great since it makes a bootable backup for you, unlike Time Machine. I highly recommend it.

Otherwise you're good to go. The only suggestions I have are to buy an SSD for even more performance, and to upgrade your graphics card, you can get a PC 5770 or something for really cheap and it works great.