EDIT (2015-11-14): Please note that this post was made in 2011. At that time, this was the only solution. Comments suggest there are better ways now. I have not investigated. Current project involves moving some KVM VMs from file storage to block storage. This is basically converting the .qcow2 files to LVM LVs. It was surprisingly simple. First, we need to get an idea of how much space our VM uses.
Recently I learned a couple of tricks from a gentleman that goes by the handle of fromport. Disabling caching on the disk and using the e1000 drivers for networking. To disable caching, you add cache=’none’ to the end of the driver stanza. <disk type='block' device='disk'> <driver name='qemu' type='raw' cache='none'/> <source dev='/dev/primary/indium'/> <target dev='vda' bus='virtio'/> </disk> More info: http://www.linux-kvm.org/page/Tuning_KVM The change for networking is just as easy. Simply change the model type to e1000.
Being consistent with my preferences in life, this is not a simple task. At least, figuring it out was not a plug-and-play activity we are all used to in the VMWare world of virtualization. I want: A KVM Windows Server 2008 R2 guest installed on an LVM logical volume utilizing the VirtIO drivers for storage. The LVM portion was pretty straight forward. Create an LVM out of the free space in my PV.