I tried a different port (on a different internal sata controller) and a different power supply lead for the "missing drive" in question and it failed to recognize the drive on startup. I ordered an identical new drive from the interwebs, got her last night and plopped her in to the og sata port where I had removed the "failed" HDD. So far so normal. (All of these swaps were done with power cut)
Next, I booted the computer, the 2 7500aaks drives were detected fine, raid 1 listed as degraded as expected. However, the raid 0 array was listed as "failed" and one of the raptor drives was not detected. As a result can't boot to OS. Triple checked all the physical connections.
Edited by focusbob, 11 July 2014 - 08:35 AM.