1. How to set up System-on-multipath ?

prerequisite : udev and multipath-tools installed

here are the steps on a Debian SID system :

* add dm-mpath and dm-multipath to /etc/mkinitrd/modules
* copy $tools_dir/multipath/0[12]_* to /etc/mkinitrd/scripts
* define a friendly alias for your multipathed root disk
  (in /etc/multipath.conf). Example : "system"
* enable busybox in /etc/mkinitrd/mkinitrd.conf and set ROOT
  to any valid block-device (but not a /dev/dm-* one, due to
  an mkintrd misbelief that all dm-* are managed by LVM2)
* run mkinitrd
* in /boot/grub/menu.lst, define the root= kernel parameter
  Example : root=/dev/system1
* modify /etc/fstab to reference /dev/system* partitions

At reboot, you should see some info like :

path /dev/sda : multipath system
...
gpt: 0 slices
dos: 5 slices
reduced size of partition #2 to 63
Added system1 : 0 70685937 linear /dev/system 63
Added system2 : 0 63 linear /dev/system 7068600
Added system5 : 0 995967 linear /dev/system 70686063
...

