Nagios Support Forum

Why does the value for example the CPU load in getting smaller with the larger scale of time (day graph about 80%, week about 40% and month about 10%)?
Is there a possibility that the data were in their orginal form, regardless of the time interval?


Regards,
Jan

The graphs must scale down as the time range increases otherwise they would not be able to be displayed.

A somewhat more detailed answer is:

The reason that you are getting different values is that rrds do not use every point available for every graph, additionally most points for long time frames are actually averages of several points around that time. Along those same lines, the rrd file itself gets averaged and compressed over time, allowing it to stay the same size, but causing the data to be slightly less accurate and definitely less granular over time.

Basically, your 1 week graph is able to use much more granular points of data and display them on the same scale graph, leading to less averaging and more exact information being visible. Whereas the 1 month or longer graph has to compress much more data into the same contextual space causing averaging both in the rrd itself and on the graph to be more pronounced. So while the 80 load data point would definitely be still used in the 1 month graph, it would be averaged with many more points near by that would bring it closer to the ~1 load point, or in this case ~40 load it seems.

For the shortest explaination, the min\avg\max values are all dynamically generated from the time frame requested, and will always vary depending on data points available, and amount of averaging needed to fit said points into the far fewer points on the graph.

Please let me know if you have further questions, but hopefully that clears up why they are and should be different.

Ok in that case how to use much more granular points of data to display them in 1 week graph?

Thanks for reply


Regards,
Jan

Over time RRD based graphs average out the points between data, RRDs that were already created cannot be changed but going forward you may be able to tweak rrdtool to modify these options. We will look into this and give you some options to look at.