[mrtg] Ignoring Negative Deltas

Hector Herrera mail4hh at pobox.com
Thu May 11 06:56:14 MEST 2006


I'm monitoring an external device and the output is in the form of an
ongoing count.  MRTG works great, it calculates the delta from the
last sample and then shows the values on the graph.

The problem is when the external device resets or reaches the max
count.  The last sample is a very large number, the new sample is a
very small value.  MRTG calculates a huge negative delta.  Here is
where the problem is, those large negative values show up as a large
positive spike.

Is there someway to tell MRTG to throw away any deltas in the samples
that are negative?

or, even better,

Is there a way to tell MRTG to use 0 as the last sample if the delta
is negative?

Using AbsMax and MaxBytes is not an option because the negative spikes
are sometimes smaller than real spikes we need to see, and if we set
AbsMax or MaxBytes low enough, then our real data gets thrown out.

Thank you,

Pier Programming Services Ltd.

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