Hi David
Sorry for any confusion. Below is the info/email in quotes I received from the reseller:
"Just keep the one disk in the mac pro ( or maybe 2, so you can have a backup of your system)
Forget the raid card and internal disks
Use one of these instead -
http://www.jigsaw24.com/default.aspx?ITEM=JIGSX183ARA
Its external, so if your mac breaks then you can still get to your storage. You can also transfer it to use on a different machine. Its fast enough to cope with 3 streams of video at prores format. Costs about the same as the mac pro with internal raid and disks"