[rrd-users] Sliding Window TREND with out-of-graph data

[Bernhard Schmidt]

Hello,

I'm using rrdtool to graph a very simple single GAUGE counter (the
number of active IPv6 hosts in a part of our network) into a simple RRD
file with a stepsize of 3600 seconds and without any aggregation.

To get a better visible trend from the data I was trying to use the
TREND or TRENDNAN function with a one day and one week sliding average

rrdtool graph -l 50 -r -h 400 -w 800 ipv6.png \
	-s end-3w \
	DEF:hosts=/root/ipv6hosts.rrd:hostcount:AVERAGE \
	CDEF:hosts1d=hosts,86400,TREND \
	CDEF:hosts1w=hosts,604800,TREND \
	LINE2:hosts#0000ff:Hosts \
	LINE1:hosts1w#ff0000 \
	LINE1:hosts1d#00ff00

As you can see in the resulting graphs for the 1-week, 2-week and 3-week
graphs at

http://svr02.teleport-iabg.de/~bschmidt/ipv6-1w.png
http://svr02.teleport-iabg.de/~bschmidt/ipv6-2w.png
http://svr02.teleport-iabg.de/~bschmidt/ipv6-3w.png

the sliding window for one week (red line) is not available in the first
week of the graph, even though there is older data in the RRD file. Same
for the daily trend which is not available in the first 24h of the
graph. Is this expected or a bug? TRENDNAN in more recent rrdtool
versions doesn't help. This is rrdtool 1.3.1.

Regards,
Bernhard