On Thu, Jul 11, 2019 at 16:46:29 +0200, Julian Sternberg wrote: Hi, at first I'd like to ask you to CC the libvirt-users or libvir-list with such kind of questions (questions implying regression of behaviour are okay on the development list). I've CC'd libvirt-users with this reply to archive this. Also I'd strongly encourage you _not_ to use HTML formatting on thechnical communications. As you can see I'm using a plain-text mail client and it messes up. That one does not seem to be related to your issue. It simply assumes that when starting a qemu process (so nothing really related to any of the vol-* and pool-* virsh APIs) when the disk is referencing a volume from the storage driver and the referenced volume is a directory, then we assume that qemu should use 'fat' as the driver. I'll have to cut off everything here and replace it with a non-HTML version so there might be weird quoting: I've looked at the git history and didn't find anything that could be related here unfortunately. I'm also not very familiar with RBD in libvirt. So this is really weird. The error message is produced if the target format is not 'raw' but the above command clearly supplies it. I'd suggest you collect debug logs while trying both and attach them here. Unfortunately I don't see what could be wrong here.