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
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