__SummaryInfo__
contains the information you need to calculate the averages of all metric values in the cluster. The rrd files there have two data sources, sum
for the sum of the metric values over all hosts and num
for the number of hosts that reported that metric.
You can calculate the average by dividing sum
by num
in an rrdtool CDEF statement:
DEF:sum=nameOfYour.rrd:sum:AVERAGE
DEF:num=nameOfYour.rrd:num:AVERAGE
CDEF:average=sum,num,/
Note that data resolution will deteriorate as the data gets older (more data is added).