On Mon, Jul 15, 2013 at 01:55:18PM +0200, Florian Weimer wrote: > On 07/15/2013 01:47 PM, Daniel P. Berrange wrote: > >Updating to qcow2 to support xz (or some other algo) as a built-in > >compression choice would likely give better results. > > Is the compressed image still seekable? If yes, that constrains the > window/block size and limits the gains from switching compressors. Dan's answer covered one aspect of this: are qcow2 compressed images seekable, answer: yes, of course! But there's another answer for xz images. Are these seekable? Yes. Surprisingly. I've written the code for it: https://rwmj.wordpress.com/2013/06/24/xz-plugin-for-nbdkit/#content *However* you have to prepare the xz images correctly for this to happen (using the --block-size argument, see blog posting above). Images created using standard xz parameters won't be seekable. I suggest it's a good idea that we do that for the cloud images, since the penalty is only about 1% and it makes them a lot more useful if you can use them without uncompressing them. nbdkit is included in Fedora. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/ -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
