Using this: linux (hd0,msdos1)/vmlinuz-2.6.32-431.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root initrd (hd0,msdos1)/initramfs-2.6.32-431.el6.x86_64.img boot works. The snapshot conf is missing the (hd0,msdos1) part...