Comment 136 for bug 120375

You should not need to reinstall.

To solve this, you need to:
 a) live upgrade all packages (specifically, you need to upgrade grub,
mdadm, and initramfs-tools)
 b) install grub to the raid (for instance, if /dev/md0 provides your
/boot directory, you can do "grub-install /dev/md0")

Cheers,
:-Dustin