Serleejus:

ok. Finally!! i seem to have found a 4 bay hardware raid enclosure and its affordable.

 Congrats, can't find any fault in your last find, and 3ware is a very known and respectable brand when it comes to raid cards.

Very impressive. Great find Serleejus.

I wonder why they say maximum 750GB drives (at least the reviews use the word "maximum"). Their drive compatibility list includes the Hitachi A7K1000 1TB model.

Maybe they think you're at your own risk for overheating with four 1TB drives stacked.

This looks like an interesting development for this thread: CalDigit's 8-lane RAID card (ships June, '08) allows you to hardware-RAID up to four internal drives and gives you three external ports to RAID up to twelve more drives. Looks like it'll be about $550 - pretty good deal if you ask me.

http://www.caldigit.com/RAIDCard/raidcard_index.html

So...mount your boot drive in the extra optical bay (see below) and place 4 x 1TB drives in the Mac Pro factory bays, and you could have a 4TB internal hardware-RAID for about $1500 with room to grow. Optical bay mount is here:

http://www.transintl.com/store/category.cfm?Category=2704&RequestTimeOut=500

Here's a low cost ($40) alternative if you have the slots. I use 3 cards for a 6-Way eSATA Raid-0.

Addonics 2-Port eSATAII PCI-E Controller for Mac Pro : 

http://www.amug.org/amug-web/html/amug/reviews/articles/addonics/adsa3gpx1-2em/

~400MB/sec performance with empty drives.