[mrtg] Re: Counter wrapping?

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Wed Feb 27 13:29:54 MET 2002

Barry_Young at interliant.com wrote:

> As Cisco do not seem to support 64-bit counters on this particular switch,
> I was wondering if the situation would be improved by polling the device
> more frequently ie. 60 seconds?

Yes, however: this won't make the problems go away *and* you will gain
extra problems.  There is an error in every measurement you make.  Not
only will the number of errors increase by 400%, the error-to-data ratio
will also increase.  Last but not least not every computer/OS can handle
the extra load.

The measurement errors I'm talking about include jitter and rounding
problems.  When you poll a device there is some network delay, when
you process the resulting number there may be an OS delay.  On average
these errors will cancel out each other, per interval however these
errors may cause even stronger errors.

> I have worked with mrtg for several years now and have developed some neat
> html presentation during this time, hence the reluctance to migrate to the
> rrdtool backend.  But maybe time has finally caught up with me.  Would
> rrdtool overcome this situation even with 32-bit counters?

RRDtool will correctly handle the counter wrap.  This doesn't mean it
will handle more than one counter wrap at a time so the limit of
14.3MBps is still present (for 5-minute polling periods).

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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