A data base with one data source holding three years in 5-minute resolution is only 2.5 MB size:
rrdtool create save.rrd \
--step 300 \
DS:inet_down_total:DERIVE:600:0:U \
DS:inet_down_comp1:DERIVE:600:0:U \
DS:inet_down_comp2:DERIVE:600:0:U \
DS:inet_down_other:DERIVE:600:0:U \
RRA:AVERAGE:0.5:1:315360