On Fri, Aug 24, 2012 at 09:35:01PM +0100, Paul Maunders wrote: > >> Is it possible to enable qcow2 compression when using virt-install to > >> create a new image as part of a new virtual machine? > >> > >> I've searched the manual and online, but can't find any info on this. > > > > IIRC if you create the target disk yourself (using 'qemu-img create') > > and point virt-install at the disk (--disk path=foo.qcow2,format=qcow2) > > then it should work. > > > > Rich. > > I gave it a go, but it doesn't look like the compression option is > supported with qemu-img create. > > It is supported with qemu-img convert, so I tried creating an empty > image, then converting this to be a compressed image. However, when I > installed an OS on to this image no files were compressed. Right. qemu doesn't support compression on writes, so you can't create a new disk (with no content) with compression enabled. You can only convert an existing disk with content, and I believe writes to such a disk are either entirely disabled or create uncompressed content. > I was able to get some compression working by installing a virtual > machine without compression using virt-install, stopping it, using > qemu convert -c ... to compress the image to a new image, then moving > the new image into the original location. > > 370M Aug 24 21:00 test-centos-compressed.img > 1.3G Aug 24 20:17 test-centos-uncompressed.img > > However, although the existing data was compressed, it seems that when > I started the vm, any new data appears to be stored uncompressed. I > tested this by downloading a large gzip'd wikipedia xml dump inside > the vm, and uncompressing it. See above. virt-sparsify is another option if you're just trying to create small (offline) disk images. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming blog: http://rwmj.wordpress.com Fedora now supports 80 OCaml packages (the OPEN alternative to F#) http://cocan.org/getting_started_with_ocaml_on_red_hat_and_fedora
