[Rdo-list] Creating nova instance without backing image

Pádraig Brady pbrady at redhat.com
Wed May 21 20:11:19 UTC 2014

On 05/21/2014 06:42 PM, Daniel Speichert wrote:
> Hi,
> In our OpenStack installation (Havana, RDO), we use Ceph as storage as
> Nova, Glance and Cinder backend.
> On compute nodes, instance's disks are kept on Ceph but base images are
> copied from Glance (Ceph) to local disk. This works well with small
> images of OS's.
> However, if we upload a big image (e.g. migrating bare hardware system
> to the cloud) that is only used by one instance, the image becomes the
> backing file stored locally on the compute node. Here, the compute node
> hit disk space limit because we expect all the data to reside on Ceph.
> Is there any way to tell Nova to not use backing image for an instance?
> Maybe there exists a special image property to set that tells Nova to
> copy the whole image, which would put it entirely in Ceph without a
> backing file?
> I hope this use case makes sense for and I'd appreciate if you had any
> suggestions how to resolve this issue.
> Best,
> Daniel

That's an interesting though unusual case.

So the traditional case is where one stores ideally small
image templates in glance.
  Is there any way to use something like virt-sparsify to create a
small(er) cow2 image in glance?  With the default nova config
that should result in sparse files on the compute node
(details at http://www.pixelbeat.org/docs/openstack_libvirt_images/)

There has been consideration for more efficient interaction
between glance and nova at:
That would allow glance to essentially just send an image location
to nova, and then nova (plugins) could process as desired.
However it seems that functionality is not yet completed.


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