I use an CalDigit HDPro connected with a fibre channel card directly to my MacPro 2009.
I have it set up as a Raid5 with 6TB of storage.
The way this is set up works is it has seven 750GB HDs witch information is striped across 6 of them and one is used for a kind of a backup. So if one drive fails you simply pull that one get a new one, install it then rebuild it to resync with others and off you go again with no information lost.
Also you can keep working with one drive down. Just get it replaced asap because if one more goes down at the same time then you are in trouble.
I have used this for the past two years.