[openstack-dev] [Nova] Raw vs Qcow2 images_type in nova/libvirt

Dmitry Guryanov dguryanov at parallels.com
Tue Jan 20 11:11:01 UTC 2015

On 01/20/2015 12:18 AM, Pádraig Brady wrote:
> On 19/01/15 20:41, Michael Still wrote:
>> Mostly.
>> qcow2 can do a copy on write layer, although it can be disabled IIRC.
>> So if COW is turned on, you get only the delta in the instance
>> directory when using qcow2.
>> Cheers,
>> Michael
>> On Tue, Jan 20, 2015 at 7:40 AM, Dmitry Guryanov
>> <dguryanov at parallels.com> wrote:
>>> Hello,
>>> Do I understand correctly, that both Qcow2 and Raw classes in
>>> libvirt/imagebackend.py can work with images in qcow2 format, but Raw copies
>>> the whole base image from cache to the instance's dir and Qcow2 only creates
>>> a delta (and use base image from cache)?
> Correct.  That Raw class should be renamed to Copy,
> to clarify/distinguish from CopyOnWrite.
> BTW there are some notes on these settings at:
> http://www.pixelbeat.org/docs/openstack_libvirt_images/
> Pádraig

Thanks! Excellent article.

Dmitry Guryanov

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