code: private String getDsDefStr(DsDef def) {
  		return "DS:" + def.getDsName() + ":" + def.getDsType() + ":" + def.getHeartbeat() + ":" + formatDouble(def.getMinValue()) + ":"
  				+ formatDouble(def.getMaxValue());
  	}
docs: "rrdtool create temperature.rrd --step 300 \\\n" +
  "         DS:temp:GAUGE:600:-273:5000 \\\n" +
  "         RRA:AVERAGE:0.5:1:1200 \\\n" +
  "         RRA:MIN:0.5:12:2400 \\\n" + "         RRA:MAX:0.5:12:2400 \\\n"
  + "         RRA:AVERAGE:0.5:12:2400"