RedHat Linux / RHEL 5 and previous versions have a problem with large volumes because of a boot limitation with GRUB .9x (now referred to as ‘GRUB Legacy’ which does not allow booting to volumes larger than roughly 2 terabytes. This is an issue because when you get servers with storage like a Dell PowerEdge 2950 and you load it up with a bunch of 750 gig drives and RAID 5 them, you are into the 3-4 terabyte range.
GRUB does not like dealing with such large volumes. But, rather than taking one of the drives out of the RAID and using that as boot volume, you can do a couple of other things. You can boot with an external hard drive, but that gets pretty messy.
What works well, is to get a 1 gig or so USB memory stick and during the RHEL install, put the
mount on it and leave root and the other mounts on the large RAID. GRUB will install on the USB and and long as you have that in at boot, you will be good until RH can get off their butts and bring the GRUB 2 fully into the mix.