This is a follow on from the article describing how to mirror your disks using LVM and mdadm. While I was testing booting off each mirror, I managed to screw up grub. This is how I recovered it. The procedure is slightly more complicated than if you used standard partitions due to the fact I was using both LVM and mdadm. However, it just requires a couple of extra steps.

1. Boot your PC/server from a live CD. Be sure to use a 64bit live CD if your OS is 64bit.

2. Mount the root filesystem from your server disk (in this case, a logical volume)

 mount /dev/vg-mint/root /mnt

3. Now bind the directories that grub may need

 mount --bind /dev /mnt/dev
 mount --bind /dev/pts /mnt/dev/pts
 mount --bind /proc /mnt/proc
 mount --bind /sys /mnt/sys

4. Now we need to mount /boot . However, it is a metadevice so first we need to install mdadm

 apt-get install mdadm

5. Now discover the metadevice and mount it

 mdadm --assemble --scan
 mount /dev/md0 /mnt/boot

6. chroot the /mnt environment

 chroot /mnt

7. Now fix grub (mirrors are /dev/sda & /dev/sdb in this example)

 grub-install /dev/sda
 grub-install /dev/sdb
 grub-install --recheck /dev/sda
 grub-install --recheck /dev/sdb
 update-grub

8. Now reboot