Hi, I'm trying to get KVM VMs set up right on top of DRBD, with a dedicated DRBD mirror instance on top of a dedicated pair of LVM LVs per VM - allowing, for instance, primary-secondary DRBD assignments at the same granularity as the VMs. In other words, I want to put VMs in raw format directly to the DRBD block device, just as they are commonly put to an LV block device, with the DRBD block device stacked on the LV block device. DRBD is happy to stack on an LV (just as libvirt-KVM-QEMU is happy to). But when I take an existing KVM LV, set up DRBD for it (DRBD can typically be placed on a partition with an existing file system, which it inherits), and then use "virsh edit" to replace the source dev, like so: <disk type='block' device='disk'> <driver name='qemu' type='raw'/> <source dev='/dev/VolumeGroup/SomeVolume'/> <target dev='hda' bus='ide'/> <address type='drive' controller='0' bus='0' unit='0'/> </disk> changing the center line to <source dev='/dev/drbd/by-res/SomeDom'/> (or /dev/drbdN - to which that's a symlink), then I get # virsh start sql error: Failed to start domain SomeDom error: unable to open disk path /dev/drbd/by-res/SomeDom: Wrong medium type If this were a normal file system, setting up DRBD with it, then remounting it through the DRBD device would work. But libvirt doesn't want to "mount" it. This is with virsh 0.9.12. I don't know what constitutes "Wrong medium type" here. I had thought it the general case that raw files for KVM can be written to block devices generally, which is what a DRBD device is, just as much as an LV device is. Is this then a case where I have to change something else in the XML? Or a case where it would work except that libvirt doesn't recognize that this is a media type that will work, yet is is, so that the answer would be to alter libvirt's source and recompile? Or would getting this scheme to work require the trouble of stacking things like VM LV VG PV DRBD LV VG PV DISK instead of simply like VM DRBD LV VG PV DISK Since there's a strict 1 VM-1 DRBD-1 LV correspondence, I'm hoping those extra layers won't be necessary to get DRBD into the stack. Thanks, Whit