qemu has support for ceph's "rbd" ( rados block device). you create an image of a particular size using the ceph tools, then when you create a vm xml definition

qemu has support for ceph's "rbd" ( rados block device). you create an image of a particular size using the ceph tools, then when you create a vm xml definition you specify and rbd disk. ( see here http://libvirt.org/formatdomain.html#elementsDisks http://libvirt.org/formatdomain.html#elementsDisks ) finally, when the vm is booted you can use that block device like any other machine. for first install it will be empty ( need to attach a cdrom image to get going ) then youncan start making snapshots for "thin provisioning" using copy on write clones ...very sweet stuff :) re performance ...i think its good, but i have heard its not as good as expensive proprietary systems. the product we're building is around storage analytics on open source. ..so eventually well know more :)