A small downside is that the GRUB stage1 information in the MBR can be overwritten by the second install. In our example, Red Hat is installed on the first disk, and Debian is installed on the second. After Debian is installed, however, the Debian GRUB menu is displayed instead of the Red Hat menu that we are used to and that has been customized for our installation.
Let's see how we can solve this issue -
Boot to grub CLI
The root (hd0,0) command sets the (hd0,0) partition as the location of the boot directory. This command tells GRUB in which partition the stage2 and grub.conf or menu.lst files are located.
Both disks should have this file. In this instance, GRUB shows the stage1 file from the second disk.Because we want GRUB to format the MBR on the first disk, /dev/hd0 is used.
That's it! The whole process should look like this :