# [rrd-users] Question with 1-hour samples

Simon Hobson linux at thehobsons.co.uk
Thu Jan 20 17:51:13 CET 2011

```Jason wrote:

>So for the following data example:
>
>Let's say that I have created a brand new *.rrd and collected data for
>the first three hours using the 300 second step period, with 12 steps
>filling one CDP.  The PDPs are filled into CDPs in the following way:
>
>PDP 1 values for first hour sampling:
>(10, 10, 10, 10, 10, 10, 20, 20, 20, 20, 20, 20)
>CDP 1 AVERAGE consolidation:  15
>
>PDP 2 values for second hour sampling:
>(20, 20, 20, 20, 20, 20, 30, 30, 30, 30, 30, 30)
>CDP 2 AVERAGE consolidation:  25
>
>PDP 3 values for third hour sampling:
>(10, 10, 10, 10, 10, 10, 30, 30, 30, 30, 30, 30)
>CDP 3 AVERAGE consolidation:  20
>
>Firstly, is this not correct?

Looks right to me

>Next question:
>Let's say there are two RRDs for my Data Source - the first one is to
>hold 14 days (336 rows) of CDPs and the second one holds 60 days (1440
>rows) of CDPs.
>
>When I graph the AVERAGE of these first three CDPs into two separate
>graphs (14 versus 60 day 1-hour average), shouldn't both of them show a
>maximum CDP of 25?  My two graphs don't show this - they are different.
>  In addition, when I GPRINT the maximum value, they are not the same
>either.  The 60 day is about 1/3 of the 14 day, for some reason.  For
>the first three hours, the MAXIMUM of the averages should be the same
>between 14 and 60 day.  Right?
>
>This is how I am doing the graphing:
>

Bear in mind that your max is not the max during the hour, it's the
maximum of the hourly average.

As to why it's not working as expected, I dunno.

here's a quick bash script I've done - fill in the values, run it
against the two files, and see what happens. Doing it this way, it's
easy to see what went in and what came out.

#!/bin/bash

start_time=`date -d "01 Jan 2011 00:00 UTC" +%s`
step=300
values=( "10" "10" "20" "30" )

time=\${start_time}

for value in \${values[@]}
do
time=\$(( \${time} + \${step} ))
echo rrdtool update "\${file}" \${time}:\${value}
done
end_time=\${time}
echo rrdtool fetch "\${file}" AVERAGE -s \${start_time} -e \${end_time}

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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```