'Return size of volume to be managed by manage_existing.
When calculating the size, round up to the next GB.
:param volume:       Cinder volume to manage
:param existing_ref: Driver-specific information used to identify a
volume'

def manage_existing_get_size(self, volume, existing_ref):

    existing_volume_name = self._get_existing_volume_ref_name(existing_ref)
    data = self._get_volume_info(existing_volume_name)
    return data['size']
