[mrtg] Re: Problems with peaks

Steve Shipway s.shipway at auckland.ac.nz
Mon Jan 30 22:28:27 MET 2006

> I've something read about the '95 percentile', which prevents 
> the graphics building some peaks.
> I have some peaks during nightly backup, so the graphics are 
> looking strange at the rest of the day.

This is not what the 95th percentile is.  The 95th percentile is the minimum
value below which 95% of the datapoints lie.  It is used as an indicator of
the amount of bandwidth generally required for a certain data pattern.  By
comparison, the average is the 50% percentile.

The new rrd v1.2.x apparently will maintain a running 95th percentile value
which could be plotted to achieve a smoothing, but this would require
modification of the rrd files plus custom graph parameters for your
frontend.  This would give misleading values on the graph, though - although
you want to ignore spikes due to backups, you dont want to ignore *all*
spikes... some may be a real network problem.

> how can i implement this to prevent showing these peaks ?

(1) set thresholds to ignore these high values (bad - ignores problem data
(2) use the killspike program to remove them after the fact (awkward)
(3) use the rescale function in the routers2 frontend to view the graph
differently (requires using a specific frontend)
(4) force the graph to have a set max on the y axis (requires custom graph


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