[rrd-users] Help with creating an rrd-db

Koenraad Lelong rrd-tool1 at de-brouwerij.be
Mon Jul 20 16:40:38 CEST 2009

I'm having troubles creating an rrd-db. I hope someone can point me in 
the right direction.
I have a photovoltaic system I'm monitoring. At the moment I can make 
nice graphs of the instantanious production, this means the power the 
station is generating at a given moment. I poll the station about every 
15 seconds.
Another value is the total produced energy. This is where my problem is. 
I created this rrd :
rrdtool create etot.rrd --start 1206187000 --step 15 \
DS:ETOT:COUNTER:30:0:10000000 \
RRA:MAX:0.5:1:5760 \
RRA:MAX:0.5:5760:7 \
RRA:MAX:0.5:5760:31 \

What I would like to get is graphs of the energy-production per day, so 
the value "last measurement of the day" - "first measurement of the 
day", displayed per week, month, year.

When I enter the values (also at 15 seconds interval), I get unexpected 
results in the graph. I get results mostly is the milli-range, while all 
the values I enter are by now 4.5 million (Wh produced).

What am I missing here ? When I dump the rrd, I also get values in the 
milli-range. Could it be that the values in the rrd are the difference 
between the input values ? The values that are entered don't change much 
in 15 seconds, many times, the difference is zero.
How can I solve this ?

Thanks for any pointers.

Koenraad Lelong.

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