CentOS 6 won’t boot/load GRUB on software RAID /dev/md0

If you’ve just installed CentOS 6 on software RAID and it won’t boot off /dev/md0, try the following:

1. Using your CentOS install media, boot in to rescue mode

2. Once you are booted in to rescue mode, select the “start shell” option

3. Enter the following command:

chroot /mnt/sysimage

4. Re-install GRUB (/dev/md0 may be different for you depending on how you configured your software RAID)

grub-install /dev/md0

5. Reboot

The above commands helped me fix this issue on CentOS 6.3 x86_64 minimal.

https://www.centosblog.com/fix-for-centos-6-wont-bootload-grub-on-software-raid-devmd0/