On 08/05/2013 12:49 AM, Joshua Harlow wrote: > Hi all, > > I was looking into newer formats for images for qemu/KVM and noticed a new > one called qed,
> > http://wiki.qemu.org/Features/QED I don't see any active development of QED format. > > Has anyone in the openstack qemu/KVM users had any experience trying this > format out? Was it better or worse than qcow2?? Short: I haven't tried it. However, from upstream QEMU's git master branch, last commit to QED was about an year ago. Long: ==== I strongly recommend qcow2 - it is actively being developed upstream, and is also relatively widely used. Also, QCOW2 can give you near raw performance. - You can use the preallocation=metadata flag to extract better I/O performance $ DISKIMAGE=/export/foobar.qcow2 $ qemu-img create -f qcow2 -o preallocation=metadata $DISKIMAGE 10G - Further, you can even 'fallocate' the qcow2 image(which allocates all the blocks to the file ahead of time) $ fallocate -l `ls -al $diskimage | awk '{print $5}'` $DISKIMAGE Related feature in OpenStack - https://blueprints.launchpad.net/nova/+spec/preallocated-images > > Be neat to know if it really is better from real usage/experience :) FWIW, I extensively use qcow2 in my test lab, and with preallocation and 'fallocate', I get pretty much near raw performance and additionally all the qcow2 features like overlay images/backing files, snapshots, sparse-files etc. Versio3 of qcow2 is has two additional new features/performance optimizations for some usecases: - lazy_refcounts -- it's essentially a performance optimization interesting only when using 'cache=writethrough' . Useful when guest crashes or powers off. - NOTE: The above feature is not much helpful when using 'cache=none/writeback' (which is usually preferred). It can be invoked as below: $ qemu-img create -f qcow2 -o compat=1.1,lazy_refcounts=on a.qcow2 10G $ qemu-system-x86_64 -drive if=virtio,file=a.qcow2,cache=writethrough - Zero clusters -- Useful for image streaming over slow network connections. -- /kashyap _______________________________________________ OpenStack-dev mailing list [email protected] http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
