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I am setting up a Collectd server along with drraw. When I go to graph out a data source I am asked to select "min, avr, max" and "last"

I take that the last option is the LATEST data point (but it's missing from my collectd data files or drraw complains).

So what does Min, Avr, Max mean... when I am graphing shouldn't I be graphing the last?

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2 Answers 2

Those are consolidation functions of RRDtool. You can find out more from the rrdcreate manpage

Quoting from the manpage:

The data is also processed with the consolidation function (CF) of the archive. There are several consolidation functions that consolidate primary data points via an aggregate function: AVERAGE, MIN, MAX, LAST.

AVERAGE the average of the data points is stored.

MIN the smallest of the data points is stored.

MAX the largest of the data points is stored.

LAST the last data points is used.

I recommend you read through all of the mapage in order to get a better understanding of how rrdtool stores your data.

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LAST is a single data point and such probably isn't a good value to read or graph for monitoring purposes as it could be an anomalous result. As a for instance, if monitoring CPU use generally or of a particular process you take the "LAST" reading that reading could be taken during a sudden short burst of activity during an otherwise quiet reporting period.

AVERAGE is usually a much more useful reading for monitoring purposes, if the reporting period is not too high, with MIN and MAX providing upper and lower bounds which are useful for more detailed analysis (the average of a given reading will not be right in the middle of MIN and MAX in most cases).

AS icantbelieveitsnotlinux suggested before me, the RRDTool documentation should help you better understand how collectd stores your data.

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