I swapped out my 1 TB Hard drive for a Seagate 1.5 TB one. The mac pro recognizes them and the disc utility finds no problems with them. I tried raiding them together and MAC OS X 10.5 wouldn't install, tried to install it just on one drive and it kept getting an error. Tried both options multiple times and it seems like at random points it seems to bring up the yellow triangle and says error. After the errors the drives no longer show up in disc utility. I formatted the drives before trying to install os x. Its not just the disc either because I used a leopard install disc and also the 2 that came with my computer. Anybody have an idea of whats going on?