Comment 3 for bug 1457517

You are right. There is no need to check the disk in flavor if boot from volume.

But in nova code, it is a common function :
https://github.com/openstack/nova/blob/master/nova/compute/api.py#L651

If boot from image,we must check it. So there is two ways to solve this problem.One is to check whether is boot from volume before _check_requested_image().The other one is to check it in _check_requested_image() to avoid it.

I have submit a patch about this problem with the second way.You can test whether it's solved or not :)