libivrt+xen does not support copy on write images

[Alvaro Lopez]

The blktap2 (http://wiki.xen.org/wiki/Blktap2) does not support qcow2 images. We should check if libvirt+xen is being used, and raise an error if nova is configured to use cow images.

[Alvaro Lopez (aloga)]

Actually this is more complicated (see http://lists.xen.org/archives/html/xen-devel/2011-10/msg01131.html).

 - blktap2 driver does not support qcow2, but qdisk does.
 - pygrub is not able to read qcow images.
 - pv-grub is able to read them, but it is not distributed with Ubuntu and Debian.

[Alvaro Lopez (aloga)]

This is related to https://bugs.launchpad.net/nova/+bug/1326238

The only way to use "qcow2" images is to use the "qemu" (qdisk) driver.

[Markus Zoeller (markus_z) (mzoeller)]

This wishlist bug has been open a year without any activity. I'm going
to move it to "Opinion / Wishlist", which is an easily-obtainable queue
of older requests that have come on. If you decide to work on this
consider using a blueprint [1] (with a spec [2]). I'll recommend to
read [3] if not yet done.

If there are any questions left, feel free to contact me (markus_z)
in the IRC channel #openstack-nova

References:
[1] https://blueprints.launchpad.net/nova/
[2] https://github.com/openstack/nova-specs
[3] https://wiki.openstack.org/wiki/Blueprints