I think a good way to get that is to shrink the filesystem of the original disk, shrink the disk itself and convert the file-based image to the LV like you do.
Once done, you can extend the LV and the filesystem back to what it was before the process if needed.
Other than that, I don't know a way to get what you want with the current tools.
Thanks Nicholas, the above seems to have worked. Quite a few steps, though - so prone to error ... When you say 'tools' I think you mean that qemu-img cannot at the moment support conversion to thin LVs. Edoardo Comar Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU