xen not booting from lvm

[David Brownlee <abs%absd.org@localhost>]

I'm having an issue trying to move an existing xen guest from a file
to lvm. The config file is below. The /dev/vg0/fooarchive,raw is
fractionally larger than the original file (lvm rounded it up to 14G),
and I've dd'ed across the data (reported exact size of original file
transferred) and verified at least the start is identical (re-run dd
and running a cmp now)

name = "fooarchive"
memory = "1000"
disk = [ '/dev/vg0/fooarchive,raw,xvda,rw' ]
# disk = [ '/opt/xen/fooarchive,raw,xvda,rw' ]
vif = [ 'mac=02:00:00:00:01:04, bridge=bridge0', ]
bootloader = "/usr/pkg/bin/pygrub"
vcpus = 1

The image is a 32bit Ubuntu 14.0 LTS guest. Booting from the /opt/xen
runs fine, while from /dev/vg0 shows the Ubuntu boot menu (Press enter
to boot the selected OS...) then hangs. Running on NetBSD-7 STABLE
from 8th Feb. amd64, xen 45-4.5.2

Has anyone seen anything similar or have any ideas?

Thanks