You already mounted /dev/mapper/VolGroup00-LogVol00 as root (/)
that's not possible..
You should umount /dev/mapper/VolGroup00-LogVol00 and remount /dev/drbd0 as /
though if you you use drbd for you root device, i think you should be sure you have it in your initrd.img so you can boot from it .. still i think it's a strange setup. Let's say if your server crashes, the other will take over, now you're not able to (re)boot the first server anymore, because you can't have 2 primary nodes (it's possible, but you'll break everything)