qcow2 version woes

[Mo Morsi]

On 03/06/2015 12:00 PM, Kashyap Chamarthy wrote:
> On Thu, Mar 05, 2015 at 11:48:08AM -0700, Mike Ruckman wrote:
>> Fellow cloudies,
>>
>> The recent builds of our images are v3 qcow2 (also known as qcow3).
>> This presents a problem for our testing, since the openstack instances
>> we have access to don't support v3, only v2. The only difference
>> between v2 and v3 are some performance enhancements -
> Right, just some details on the said performance enhancements in QCOW2
> v3 format, from my notes (about a year old) from an earlier discussion
> w/ some QEMU developers, the two new features in v3 of QCOW2:
>
>    (1) lazy_refcounts -- A performance optimization interesting only when
>    using 'cache=writethrough'. Useful when guest crashes or powers off.
>    
>    (2) Zero clusters -- Useful for (disk) image streaming over slow
>    networks.
>
>

Perhaps of interest:

http://talk.manageiq.org/t/qcow-image-format-versions-2-3-analysis/491

   -Mo