What do you see after a few days with:

rrdtool dump /var/nedi/rrd/charon/system.rrd

I see:

<!-- 2005-02-16 01:00:00 CET / 1108512000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

<!-- 2005-02-26 01:00:00 CET / 1109376000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

...

<!-- 2012-01-21 01:00:00 CET / 1327104000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

<!-- 2012-01-31 01:00:00 CET / 1327968000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

<!-- 2012-02-10 01:00:00 CET / 1328832000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

<!-- 2012-02-20 01:00:00 CET / 1329696000 --> <row><v> NaN </v><v> NaN </v><v> NaN </v><v> NaN </v></row>

This system has been installed in 2012. It does not make any difference when I run this comman.

Btw. Today at 8, all graphs were white again. The first locations are now discovered by the cron job and show their graphs.