[openstack-dev] Fedora cloud image compression format

Adam Young ayoung at redhat.com
Mon Mar 16 13:50:48 UTC 2015

We had the following exchange on the Fedora Cloud list, but I think it 
now more properly belongs here;

On 03/12/2015 12:37 PM, Daniel P. Berrange wrote:
> On Thu, Mar 12, 2015 at 12:17:06PM -0400, Adam Young wrote:
>> So, it looks like xz is not supported by OpenStack.
>> "So what" you say "OpenStack should use QCOW anyway."
>> Not with Ceph.  Ceph does its own COW semantics with raw, and the qcow.
>> formats are not supported.  (Yes that is a regular expression dot there)
> The backends used in libvirt are supposed to be agnositic to the format
> of the image uploaded to glance. ie if the image in glance is stored
> in qcow2, but the backend is ceph, then Nova ought to be converting the
> qcow2 image to raw format on the fly, because the user shouldn't be
> exposed to details of the storage backend's capability. So if ceph
> has trouble if people upload qcow, then that's a bug in openstack that
> needs fixing.

I know Flavio Percoco has a working conversion mechanism now in Glance.


> Adding support for uploading xz compressed raw images sounds like a
> pretty good idea too, as it'd reduce the upload time. Glance could
> transparantly decompress it, or leave decompression to Nova.
Are there any library issues that make xz not a practical-to-support format?

>>    And, this is a pretty big use case.  IS there some way we can convert the
>> compression to a format supported by OpenStack, either .zip or .tar.gz
>> (yes, tar for some reason) or produce that as well as the xz format?
> Regards,
> Daniel

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