Assuming a full backup of the NODE ganeti node exists on backup.tld, here are the steps to resurect it on a new disk:
 * boot on a live CD with the same architecture as NODE
 * fdisk /dev/sda
 * create sda1 root 20GB, sda2 swap XGB (amount of RAM), sda3 LVM
 * reboot so that it is taken into account (in case it is ignored  because the disk is considered active, fdisk will tell)
 * mke2fs -t ext4 /dev/sda1 ; tune2fs -i 300 -c 300 -m 0 /dev/sda1
 * mount /dev/sda1 /mnt
 * ssh -A root@backup.tld
 * rsync -avHz --numeric-ids backup.tld:/NODE/ /mnt/
 * vi /mnt/etc/network/interface and update eth0 according to what ifconfig eth0 says
 * chroot /mnt
 * grub-install /dev/sda
 * mkdir /sys /proc
 * mount -t proc none /proc 
 * vgreduce --removemissing all
 * vgremove all
 * rm -fr /dev/all
 * pvcreate /dev/sda3 (assuming it is LVM type)
 * vgcreate all /dev/sda3
 * pvremove /dev/XXX (this is assuming the disk layout on the new machine is different from the one on the previous machine)
 * vi /mnt/etc/fstab # fix whatever needs to be
 * reboot on root with a network kernel http://guides.ovh.com/KernelNetboot
 * update-grub
 * on OVH manager switch back to hd boot
 * reboot
 * update /etc/hosts with the latest from another active host of the cluster
 * update all other hosts /etc/hosts with the IP of the newly resurected host
 * edit /etc/shorewall/params.local and set MAIN to z2-X.pokersource.info and FAILOVER to z2-X1.pokersource.info
 * cd /etc/dhcp3 ; hg pull ; hg update ; /etc/init.d/dhcp3-server restart