[Openstack] [Nova][Glance] Nova imports flat images from base file despite ceph backend

melanie witt melwittt at gmail.com
Sat Oct 13 00:17:12 UTC 2018

On Fri, 12 Oct 2018 21:50:27 +0000, Eugen Block wrote:
> I would consider this thread as closed. After I learned that nova
> imports flat images if the image's disk-format is not "raw" I tested
> some different scenarios to understand more about this topic. I still
> couldn't explain why nova did that in the specific case as I was sure
> the image's format was raw (the image has been deleted in the meantime
> but I can see in the database that the image's disk-format was indeed
> "raw").

Thanks for sharing that info. The reason I suggested that maybe the 
original image wasn't created with 'raw' format (example, with 'qemu-img 
create -f raw ...') was because I have made that mistake before in the 
past. :P It is possible to upload an image to glance that is not format 
'raw' and also specify to glance that it _is_ indeed 'raw' (I used the 
openstack CLI when I did the image upload). In that case, you will see 
nova download the image instead of doing ceph CoW clone.

> But a couple of days ago I encountered the same problem. I tried to
> upload an image from volume via Horizon dashboard (where a dropdown
> exists to choose disk-format) and the preselected value was indeed
> "qcow2" instead of "raw". I have no idea*why*  it was different from
> the default "raw" but this could have happened last week, too, althoug
> according to the database entry it should not have happened. Anyway,
> now I know the reason why some ephemeral disks are flat, I just can't
> tell how Horizon selects the format, but that's enough research for
> now. If I find out more I'll report back.

Sure, let us know if you notice anything else unusual.


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