[rrd-users] Problem: nan, timestamps ans step

[Lennart Koopmann]

Hello everyone,

i have a problem with RRDTool. I have read the tutorials and think to know 
the syntax and usage of rrdtool now. But i have a problem with my 
understanding of the "step" option! The tutorials don't explain that very 
well.

I have a MySQL database filled with sensor values and its corresponding 
timestamps. I have written a little script that reads these values and 
creates the "/usr/bin/rrdtool update" commands to fill them to a rrd. (and 
executes it)

I created a rrd:
rrdtool create test.rrd --start 1198454571 --step 60 
DS:procs:GAUGE:600:0:1000 RRA:AVERAGE:0.5:1:100

And my script executed this commands:

/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454571:257
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454631:258
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454691:256
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454751:255
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454811:256
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454871:259
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454931:258
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198454991:257
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198455051:257
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198455111:255
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198455171:255
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198455231:256
/usr/bin/rrdtool update /var/lib/test/graphs/test.rrd 1198455291:256

Now i try to fetch the data:

rrdtool fetch test.rrd --start 1198454571 AVERAGE

1198454580: nan
1198454640: nan
1198454700: nan
1198454760: nan
1198454820: nan
1198454880: nan
1198454940: nan
1198455000: nan
1198455060: nan
1198455120: nan
1198455180: nan
1198455240: nan
1198455300: nan
1198455360: nan

What went wrong? I am sure the graph won't display anything useful so i 
don't even create one.

When i look at the timestamps i think i totally misunderstood the step and 
start option.

Can anybody help me?

Thank you and merry christmas!
Lennart