# File lib/vagrant-libvirt/config.rb, line 283
      def _get_device(disks)
        # skip existing devices and also the first one (vda)
        exist = disks.collect { |x| x[:device] } + [1.vdev.to_s]
        skip = 1 # we're 1 based, not 0 based...
        loop do
          dev = skip.vdev # get lettered device
          return dev unless exist.include?(dev)
          skip += 1
        end
      end