On Mon, Jul 23, 2012 at 10:41:55AM +0100, Richard W.M. Jones wrote: > On Mon, Jul 23, 2012 at 10:28:57AM +0100, Daniel P. Berrange wrote: > > I agree with the quoted text that libvirt should define a > > directory to use for the transient disks under /var/lib/libvirt/images > > perhaps, and just use 'qemu-img create' to create that, and the > > unlink it once QEMU has started up, so we can auto-cleanup > > on QEMU shutdown. > > One issue here is that 'qemu-img create' is slow. 0.4 seconds to > create a qcow2 file backing another file (ie. per readonly disk, and > programs like virt-df may open dozens of readonly disks). > > I looked at the strace output and it seems the slowness is just > overhead from the machinery of qemu's coroutines, and not connected > with writing the qcow2 file, which is presumably why the qemu > snapshot=on option is not noticably slow. Other options available could be - Enhance QEMU to allow a snapshot directory to be specified - Make libvirt actually create the empty QCow2 file. The QEMU people will probably say this is evil, but the knowledge required to a create an empty qcow2 file pointing to a backing file is pretty tiny. Or we could even do both, using the former for new enough QEMU and the latter only for older QEMU Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list