Default block device mapping seems to be an issue with RHOS8 to v12 when using nova boot and adding a blank volume. I was able to boot of a VHD stored in Glance, but specifying a blank volume seems to break since /dev/sdb isnt valid on HypV. Not using any iSCSI here just a D: drive w an Instances folder.
nova boot --image source--block-device source=blank,dest=volume,size=25,shutdown=preserve --nic net-id=uuid --flavor 3 name
from nova-compute.log Booting with volume None at /dev/sdb
