Preseed: Expert recipe with LVM in partman-auto fails to format disk

[Antoine Mazeas <antoine@karthanis.net>]

Dear Debian Users,

For quite some time, I am failing to make partman process a custom 
expert recipe during an unattended (preseeded) installation.

I am setting up a VM with an 8000 MB disk space (single disk) that I 
want to partition using LVM. However, every time the recipe runs, I end 
up getting an error from partman which I don't understand:

> Failed to partition the selected disk

>This happened because the selected recipe does not contain any 
partition that can be created on LVM volumes.

Here's my full recipe and other partman options

# partitions
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
d-i partman-auto/method string lvm
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-lvm/confirm boolean true
d-i partman-lvm/confirm_nooverwrite boolean true
d-i partman-auto-lvm/new_vg_name string vg
d-i partman-md/device_remove_md boolean true
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/default_filesystem string ext4
d-i partman-auto/expert_recipe string \
  large-varlibdocker :: \
    512 512 512 ext4 $primary{ } $lvmignore{ } label{ boot } method{ 
format } format{ } use_filesystem{ } filesystem{ ext4 } mountpoint{ 
/boot } . \
    2048 2048 2048 linux-swap $lvm_ok{ } method{ swap } format{ } 
in_vg{ vg } . \
    1024 1024 1024 ext4 $lvm_ok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } in_vg{ vg } lv_name{ root } 
mountpoint{ / } . \
    512 512 512 ext4 $lvm_ok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } in_vg{ vg } lv_name{ tmp } 
mountpoint{ /tmp } . \
    512 512 512 ext4 $lvm_ok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } in_vg{ vg } lv_name{ varlog } 
mountpoint{ /var/log } . \
    512 512 512 ext4 $lvm_ok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } in_vg{ vg } lv_name{ backup } 
mountpoint{ /backup } . \
    512 513 -1 ext4 $lvm_ok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } in_vg{ vg } lv_name{ varlibdocker } 
mountpoint{ /var/lib/docker } .


For sanity's sake, I could get this recipe to work... (inspired from 
lists.debian.org/debian-user/2014/12/msg00651.html):

d-i partman-auto/expert_recipe string \
  lvm-multi :: \
    512 512 512 ext2 $primary{ } label{ boot } method{ format } format{ 
} use_filesystem{ } filesystem{ ext2 } mountpoint{ /boot } . \
    2048 4096 4096 linux-swap $lvmok{ } method{ swap } format{ } . \
    1024 20480 20480 ext4  $lvmok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } mountpoint{ / } . \
    1024 20480 20480 ext4  $lvmok{ } method{ format } format{ } 
use_filesystem{ } filesystem{ ext4 } mountpoint{ /var } . \
    64 64 64 ext4  $lvmok{ } method{ format } format{ } use_filesystem{ 
} filesystem{ ext4 } mountpoint{ /home } .


But I seem to be unable to modify it any further (like adding a 
partition) without triggering the error mentioned above.

Any help or pointer appreciated...

Antoine