Les Mikesell wrote:
Centos doesn't install grub correctly for RAID. Just do the install by hand: http://www.dirigo.net/tuxTips/avoidingProblems/GrubMdMbr.php You may have to experiment to see how to make the second drive boot if the first one fails. With SCSI, the drives shift up in both the grub and linux device names. With IDE they don't. I'm not sure about SATA. In the worst case you could change the cable and repeat the grub install procedure if you get the 2nd drive wrong and your primary fails
I had to boot into rescue mode from the cd and chrooted the environment. Followed the example from the link above and it fixed the problem. Many thanks. I've been pretty lucky with grub these last couple of years and haven't had to delve into it this deeply before.