Something

        RRDs::graph("$outpath/df".$i.".png",
                    $graph_opts,
                    $more_opts,
                    "DEF:d".$i."=".$rrd_file.":d".$i.":AVERAGE",
                    "VDEF:d".$i."max=d".$i.",MAXIMUM",
                    "VDEF:d".$i."min=d".$i.",MINIMUM",
                    "VDEF:d".$i."avg=d".$i.",AVERAGE",
                    "VDEF:d".$i."last=d".$i.",LAST",
                    "COMMENT:\"                    max       min        avg       last\\n\"",
                    "LINE1:d".$i."\"#FF0000:\"".$mountpoints[$i-1]." (".$disksize[$i-1].")",
                    "GPRINT:d".$i."max:\"%5.1lf %sB\"",
                    "GPRINT:d".$i."min:\"%5.1lf %sB\"",
                    "GPRINT:d".$i."avg:\"%5.1lf %sB\"",
                    "GPRINT:d".$i."last:\"%5.1lf %sB\"");

print join(" ", (..));

pics/io/df1.png -w 400 -h 135 -E VRULE:1190736000#EFA413 -t 'io: used disk space' -b 1024 -v 'Bytes' -A DEF:d1=data/storage.rrd:d1:AVERAGE VDEF:d1max=d1,MAXIMUM VDEF:d1min=d1,MINIMUM VDEF:d1avg=d1,AVERAGE VDEF:d1last=d1,LAST COMMENT:"                    max       min        avg       last\n" LINE1:d1"#FF0000:"/ (450M) GPRINT:d1max:"%5.1lf %sB" GPRINT:d1min:"%5.1lf %sB" GPRINT:d1avg:"%5.1lf %sB" GPRINT:d1last:"%5.1lf %sB"