When reading a libvirt guest, virt-v2v uses libvirt metadata to determine the on-disk format used by the guest. However, this data is only meaningful for libvirt pools of type 'dir', 'fs' and 'netfs'. If a guest used a different type of storage pool, virt-v2v would attempt to interpret this meaningless data as a format type.
virt-v2v was unable to convert libvirt guests which used storage pools of types other than 'dir', 'fs' and 'netfs'.
virt-v2v now only uses volume format metadata from storage pools of type 'dir', 'fs' and 'netfs'. All other storage pools can only hold raw data, so the format is assumed to be 'raw'.
virt-v2v can now convert libvirt guests using any supported storage pool type.