[rrd-users] Graph will be inaccurate when there is huge value

Tobias Oetiker tobi at oetiker.ch
Fri Nov 19 15:36:03 CET 2010

Hi Frankie,

Tuesday frankie wrote:

> Hi All,
> I have a rrdtool program to query the snmp and graph the network performance
> graph.
> However , I find that those network port with huge usage (Let say more than
> 600Mb) , and then the graph can not reflect the actual usage of the network
> port. But those network port with normal usage are working fine.
> I read this page
> (http://www.mrtg.org/rrdtool/tut/rrdtutorial.en.html#___top). I wild guess
> that the problem may related to Counter Wraps mentioned in the page. Any
> suggestion or comment on it?

rrdtool does recognize counter wraps in 32 and 64bit counters, but
if a counter wraps multiple times between update intervals, then
rrdtool will not be able to give accurate results anymore ... to
prevent this:

  * Use 64bit counters

  * Read counters frequently

  * If the counter wraps at odd times, use the DERIVE ds type with
    a minimum value of 0. This will cause counter wraps to cause
    'unknowns' to be logged.


> Thanks,
> frankie

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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