The purpose of an RRD is to store data in the round robin archives (RRA). An archive consists of a number of
data values or statistics for each of the defined data-sources (DS) and is defined with an RRA line.
When data is entered into an RRD, it is first fit into time slots of the length defined with the -s option,
thus becoming a primary data point.
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.
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.
the last data points is used.
Note that data aggregation inevitably leads to loss of precision and information. The trick is to pick the
aggregate function such that the interesting properties of your data is kept across the aggregation process.
The format of RRA line for these consolidation functions is:
RRA:AVERAGE | MIN | MAX | LAST:xff:steps:rows
xff The xfiles factor defines what part of a consolidation interval may be made up from *UNKNOWN* data while
the consolidated value is still regarded as known. It is given as the ratio of allowed *UNKNOWN* PDPs to the
number of PDPs in the interval. Thus, it ranges from 0 to 1 (exclusive).
steps defines how many of these primary data points are used to build a consolidated data point which then goes
into the archive.
rows defines how many generations of data values are kept in an RRA. Obviously, this has to be greater than