qcow2 version woes

Kashyap Chamarthy kchamart at redhat.com
Sat Mar 7 21:49:48 UTC 2015


On Fri, Mar 06, 2015 at 03:48:40PM -0500, Mo Morsi wrote:
> 
> 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

Yep, it is interesting.

Thanks for the pointer, Mo.

-- 
/kashyap


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