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

Pádraig Brady P at draigBrady.com
Mon Jan 19 21:18:55 UTC 2015

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:


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