Creating block devices for openstack deployment using MAAS and juju (nova-volume deployment)

You can set the block device to be a file location. If you look at the nova-volume charm readme here: http://jujucharms.com/charms/precise/nova-volume

You can see that you can set the block device to /path/to/file[|size]

So, you can configure your openstack.cfg file with something like:

nova-volume:
    # This must be a free block device that is writable on the nova-volume host.
    block-device: "/var/lib/nova-volume/volume-1.img|100G"
    overwrite: "true"

This avoids the necessity to have a separate hardware device, but of course, is not ideal for a high performance production environment.