[rrd-users] Graphs wrong after reboot - samples included

[Michael Wells]

Hi,

Can anyone help explain this? I have an RRD for my network traffic. I
get the counter value from SNMP, and plot using the graph function I
posted earlier today. Note: this is not to do with moving averages, it's
a plotting problem.

I'm finding that when I reboot, the graphs I get are fouled up. An
example of what the graph looks like before and after reboot is here:

http://www.wells.org.uk/rrdtools/before.png
http://www.wells.org.uk/rrdtools/after.png

I'm assuming that when the counter goes back to zero (after the reboot),
the fact that it's a counter implies to rrdtool update that something
has overflowed. Unfortunately, my graph doesn't recover! :-(

Any ideas?

Here is the command I used to create the rrd in the first place:

#/bin/sh

   rrdtool create rl0.rrd         \
            DS:input:COUNTER:3600:U:U  \
            DS:output:COUNTER:3600:U:U \
            RRA:AVERAGE:0.5:1:600      \
            RRA:AVERAGE:0.5:6:700      \
            RRA:AVERAGE:0.5:24:775     \
            RRA:AVERAGE:0.5:288:797    \
            RRA:MAX:0.5:1:600          \
            RRA:MAX:0.5:6:700          \
            RRA:MAX:0.5:24:775         \
            RRA:MAX:0.5:288:797

And here is the update command:

        /usr/local/bin/rrdtool update rl0.rrd N:$rl0in:$rl0out

...where $rl0in and $rl0out are obtained from these SNMP MIBs:

interfaces.ifTable.ifEntry.ifInOctets.3 
interfaces.ifTable.ifEntry.ifOutOctets.3

Both are integers, and I poll them every few minutes.

If I reset the RRDs (and throw away all old data), everything works again.
I have found these behaviour happens every time I reboot, and is
consistently the same. Thomas, help! :-)

Thanks
Michael

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