/!\ In order to test Multipath in d-i you still need a patched grub ([http://bugs.debian.org/442382 #442382]).

Multipath Support in Debian Installer:

This needs to be done to support [http://sources.redhat.com/lvm2/wiki/MultipathUsageGuide multipath]ing natively in DebianInstaller:

All the points above do have patches attached, you'll need all the ones that aren't already marked as done to get working multipath support in d-i.

Multipath Testing

To enable multipath support during installation use

    install disk-detect/multipath/enable=true

at the installer prompt. If multipathed devices are found these then show up as /dev/mapper/mpathX during installation.

Installing Grub Legacy

Since grub2 doesn't support multipath yet, you have to install a patched grub in the newly installed system. Finish the installation until you're asked to reboot. Then:

  chroot /target
  dpkg -i /tmp/grub*deb
  echo "(hd0) /dev/mapper/mpath0" > /boot/grub/device.map
  grub --device-map=/boot/grub/device.map

  root (hd0,0)
  setup (hd0)