Apparently, you can't just take a working CentOS/RHEL system, and add RAID to it. You'd think that would work, but no. You'll boot, and get a message like this:

Unable to find volume group volgroup00

Followed by things like "LVM Exiting", "Kernel Panic", and other crazies.

The issue is with /boot/initrd. Your initrd image is created at installation time. The initrd loads all sorts of stuff *before* the filesystem is loaded.... so anything necessary to load the filesystem is in it. Including things like ext3 drivers, LVM, RAID, and so on.

Well, if you don't setup RAID during your inital installation, for better or worse the RAID drivers are not added to your initrd. And if your system doesn't have RAID drivers, it's not going to be seeing the LVM on top of the RAID.

I was lucky enought to have a initrd with RAID laying around, but I also suspect there's a way to re-create it. Good luck :-)