At KVM Forum Kevin, Christoph, and I had an opportunity to get together for a Block Layer BoF. We went through the recent "roadmap" mailing list thread and touched on each proposed feature.
Here is the block layer roadmap wiki page: http://wiki.qemu.org/BlockRoadmap Kevin: I have moved the runtime WCE toggling to QEMU 1.0 since you mentioned you want it for the next release. My main take-away from the BoF was that integrating support for host block devices and storage appliances will allow us to reduce the amount of effort spent on image formats. In order to make image formats support the desired features and performance we end up implementing much of the storage stack and file systems in userspace - code that is duplicated and cannot take advantage of the existing storage stack. Storage management features are not just available in remote SAN and NAS appliances anymore. For local storage, btrfs has file-level clones and thin-dev is significantly improving LVM snapshots. Thin-dev is bringing a much more efficient and scalable snapshot model to LVM. This device-mapper feature will make LVM attractive for high performance I/O without giving up snapshot and clone features. It also supports cloning off block devices that are not in the pool (e.g. external storage, much like QEMU's backing files feature): https://github.com/jthornber/linux-2.6/tree/thin-dev This will not replace image formats overnight because image formats are still widely used and will continue to be a useful for transferring and sharing disk images. But focussing on the larger storage stack where either local LVM, btrfs, or storage appliances do the storage management means we exploit those options instead of implementing equivalent functionality ourselves. QEMU then runs with plain old raw in more cases. Stefan
