A shame, I got side tracked by other issues and have not had time to
spend on an idea I had.

2. One thing to note there is that device detection is quite dynamic.
Whatever disk with the right uuid or label is found first will likely be
the one appearing in the by-uuid or by-label dirs. And I would guess it
is not guaranteed to be the same.

4. It is maybe not doable in any way that would allow the same image
transparently work in any configuration. Especially with the sort of
setup that exposes the same storage area through two interfaces. And as
you say its is a special installation image anyway. I think the issue I
have with the extra kernel argument would be that this would be again
different than upstream which I rather would want to avoid.

Anyway, there was one thing that I had in my mind and wanted to try, but
then did not have the time to follow-up. I was wondering whether for an
image targeted for that use, it would be worth trying to come up with a
special multipath setup. In theory it should be possible to do a
priority callout that gives pv disk a higher priority than emulated
ones. This should arrange the multipath setup to create two groups and
make the pv one the active. One could use the device-mapper paths of
devices instead of uuid and theoretically it should work to have the
emulated disk used (if that comes up first) and then transparently
switch over to use the pv disk. The only pain with that is changing
partitions. One has (or had) to be careful about the partition volumes
that kpartx creates. I would try to play around with that, but I am not
sure when I get to it. So should someone else have time I'd be glad if I
would get feedback here.

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https://bugs.launchpad.net/bugs/900799

Title:
  Cloud images on kvm use wrong disks

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