The following assumes you have setup two raid devices, md0 and md1, with md0 being the /boot device and md1 being the rest of your drive space.
Hard Drives:
sda1 - Software RAID (for md0) - 500MB
sda2 - Software RAID (for md1) - Remaining space available
sdb1 - Software RAID (for md0) - 500MB
sdb2 - Software RAID (for md1) - Remaining space available
RAID Devices:
md0 - ext4 - /boot
md1 - LVM
During installation, make sure the boot loader is installed in /dev/sda (Master Boot Record (MBR).
Also make sure to install with the updates repository enabled as there seems to be a problem with dracut in CentOS 6.2 that will make all this not work.
Installing GRUB into the MBR of /dev/sdb:
So if your partitions are exactly like mine, the specific commands to install GRUB on /dev/sdb (actually, the commands below will also reinstall on /dev/sda) are:
[root@fedora4 ~]# grub
GNU GRUB version 0.95 (640K lower / 3072K upper memory)
[ Minimal BASH-like line editing is supported. For the first word, TAB
lists possible command completions. Anywhere else TAB lists the possible
completions of a device/filename.]
grub> root (hd0,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 15 sectors are embedded.
succeeded
Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2
/boot/grub/grub.conf"... succeeded
Done.
grub> root (hd1,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd1)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd1)"... 15 sectors are embedded.
succeeded
Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2
/boot/grub/grub.conf"... succeeded
Done.
grub> quit