[Rdo-list] Creating nova instance without backing image

[Pádraig Brady]

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:
https://blueprints.launchpad.net/glance/+spec/multiple-image-locations
https://blueprints.launchpad.net/nova/+spec/nova-image-zero-copy
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.

thanks,
Pádraig.