[rrd-users] Understanding of RRA's steps and rows

Simon Hobson linux at thehobsons.co.uk
Fri May 7 19:55:29 CEST 2010

rrdtool_usr wrote:
>How about this situation here:
>1. Create a RRD database with step of every 45 minutes.
>2. Then I want to create one RRA for that RRD database to store 2 weeks of
>data on every hour.
>So is the worked out RRA format correct as below?
>Can RRDTool support decimal values here?

No. There are no primary data point (PDPs) whose boundaries fall on 
the 1 hour you want consolidated data points (CDP) for. Thus for 
every CDP, there will be a gap where there is no PDP to fill it.

If you wanted data for 3/4 and 1 hour periods, you'd have to store 
PDP at least every 1/4 hour (15 min) so you could consolidate 3 of 
them to get 3/4 hour CDPs, and 4 to get 1 hour CDPs.

You do not have to store a CDP for 1 step time, so there is virtually 
no performance or storage penalty for having a step size of 15 min.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

More information about the rrd-users mailing list