Graph displays incorrect values with 3+ months are selected

[dyenom]

Fairly new to Cacti and spent an hour or so looking for an answer for this before I found it. Hopefully someone can help.

Looking at traffic on an interface for a week I get this. The traffic is peaking around 80Mbps:



If I select any timeframe more than 3 months I get this. Same device, same interface, but the traffic is shown peaking a little over 30Mpbs:



Any ideas on what could be causing this?

Thanks!

[cigamit]

Welcome to the wide world of consolidation and averaging. A little bit discussing the issue here
http://forums.cacti.net/viewtopic.php?f=8&t=35868

You have multiple different consolidations going on by default. First, graph display consolidation. If you have 5000 datapoints, but the graph is only 300 pixel wide, a consolidation happens to fit 5000 data points into 300 visual datapoints. By default it is being averaged. (Read the other topic) and until future version of Cacti its not easy to change this.

The 2nd consolidation being done is at the RRA level. When you create RRAs you are specifying which consolidation functions to use. When you progress through multiple levels of RRAs, then for instance on the AVERAGE consolidation function, after moving through 3 progressive consolidation, you are getting an AVERAGE of an AVERAGE. It just continues to average down from there. With the Max consolidation, you should be getting Max of Max, but the problem then comes in with the graph display. We don't really have a way of doing Max of Max in 0.8.8 branch. Instead when you do GPRINT or AREA, etc.. you are getting AVERAGE of MAX instead.