'Return size of volume to be managed by manage_volume.
When calculating the size, round up to the next GB.'

@proxy._trace_time
def manage_volume_get_size(self, volume, reference):

    existing_volume = reference['source-name']
    try:
        volumes = self._call_xiv_xcli('vol_list', vol=existing_volume).as_list
    except errors.XCLIError as e:
        error = (_('Fatal    error    in    vol_list:    %(details)s') % {'details': self._get_code_and_status_or_message(e)})
        LOG.error(error)
        raise self._get_exception()(error)
    if (len(volumes) != 1):
        error = (_('Volume    %(volume)s    is    not    available    on    storage') % {'volume': existing_volume})
        LOG.error(error)
        raise self._get_exception()(error)
    return float(volumes[0]['size'])
