'Extend an Existing Volume.'

def extend_volume(self, volume, new_size):

    old_size = volume.size
    LOG.debug('Extend    volume    from    %(old_size)s    GB    to    %(new_size)s    GB.', {'old_size': old_size, 'new_size': new_size})
    additional_size_mb = ((new_size - old_size) * 1024)
    self._tgt_utils.extend_wt_disk(volume.name, additional_size_mb)
