On Wed, May 09, 2012 at 11:08:13PM -0600, Jim Fehlig wrote: > Hi, > > I've been tinkering with improving Xen support in the libvirt driver and > wanted to discuss a few issues before submitting patches. > > Even the latest upstream release of Xen (4.1.x) contains a rather old > qemu, version 0.10.2, which rejects qcow2 images with cluster size > > 64K. The libvirt driver creates the COW image with cluster size of 2M. > Is this for performance reasons? Any objections to removing that option > and going with 'qemu-img create' default of 64K?
In general larger cluster size does improve the performance of qcow2. I'm not sure how much of a delta we get by going from 64k to 2M though. If there's any doubt then I guess it could be made into a configuration parameter. > In a setup with both Xen and KVM compute nodes, I've found a few options > for controlling scheduling of an instance to the correct node. One > option uses availability zones, e.g. > > # nova.conf on Xen compute nodes > node_availability_zone=xen-hosts > > # launching a Xen PV instance > nova boot --image <xen-pv-image> --availability_zone xen-hosts ... > > The other involves a recent commit adding additional capabilities for > compute nodes [1] and the vm_mode image property [2] used by the > XenServer driver to distinguish HVM vs PV images. E.g. > > # nova.conf on Xen compute nodes > additional_compute_capabilities="pv,hvm" > > # Set vm_mode property on Xen image > glance update <image-uuid> vm_mode=pv > > I prefer that latter approach since vm_mode will be needed in the > libvirt driver anyhow to create proper config for PV vs HVM instances. > Currently, the driver creates usable config for PV instances, but needs > some adjustments for HVM. Yes, tagging the image with details of its required guest ABI does seem like something we need to do to be able to properly support a choice betweeen PV & HVM images. It is not very good the way we currently just hardcode PV only for Xen usage in the libvirt driver. Regards, 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 :| _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
