Insert the first disc and go into recovery mode. Once you have a command prompt follow these instructions:
Installing Grub onto both MBRs
Since the /boot partition is a RAID, grub cannot read it to get the bootloader. It can only access physical drives. Thus, you still use (hd0,0) in this step.
You must see GRUB prompt:
If you are using a RAID 1 mirror disk system, you will want to install grub on all the disks in the system, so that when one disk fails, you are still able to boot. The find command above will list the disks, e.g.
grub> find /boot/grub/stage1
Now, if your disks are /dev/sda and /dev/sdb, do the following to install GRUB on /dev/sda MBR:
device (hd0) /dev/sda
This will install grub into the /dev/sdb MBR:
device (hd0) /dev/sdb
The device command tells grub to assume the drive is (hd0), i.e. the first disk in the system, when it is not necessarily the case. If your first disk fails, however, your second disk will then be the first disk in the system, and so the MBR will be correct.
The grub.conf does change from the normal install. The difference is in the specified root drive, it is now a RAID drive and no longer a physical drive.For example it would look like:
kernel /bzImage root=/dev/md3