if ($simple_rrd) {
        $rrd_options .= ' CDEF:' . $rrd['ds'] . $i . 'min=' . $rrd['ds'] . $i . ' ';
        $rrd_options .= ' CDEF:' . $rrd['ds'] . $i . 'max=' . $rrd['ds'] . $i . ' ';
    } else {
        $rrd_options .= ' DEF:' . $rrd['ds'] . $i . 'min=' . $rrd['filename'] . ':' . $rrd['ds'] . ':MIN ';