[rrd-users] How do I make a graph using more than one RRA?

Opex system administrator sysadmin at opex.is
Thu Apr 12 11:26:25 CEST 2007

Thank you all for your answers. Now I understand better how RRAs work. :-)

Thanks again.

Kristinn Örn Sigurðsson.

Sam Umbach wrote:
> Kristinn,
>> I've been sitting here for two days reading manuals and tutorials
>> regarding rrdtool. I think I've got pretty much things covered that I
>> need to know. There is one thing that I'm not sure how works, that is
>> how can I select which RRA to use when forming a graph?
> You can use the --step option to rrdtool graph to specify what step
> size you prefer rrdtool to use when retrieving data for the graph
> (somewhat similar to the --resolution option for rrdtool fetch,
> although I'm not sure if it is affected by the start and end time in
> the same way).
> Generally, there is no reason to care which RRA the data is being
> pulled from.  rrdtool automatically fetches the data from the highest
> resolution RRA containing the start and end times.  If you've set up
> your RRAs properly, you shouldn't need to worry which RRA the data is
> fetched from.
>> For instance:
>> rrdtool create traffictest2.rrd --step 10 DS:traffic:GAUGE:20:0:U
>> RRA:AVERAGE:0.5:30:360 RRA:AVERAGE:0.5:1:10
> This RRA setup is probably not what you wanted to do.  The second RRA
> ("RRA:AVERAGE:0.5:1:10") only stores 10 rows of 1 step (10 seconds)
> each; this will store data for only the last 100 seconds.  The first
> RRA ("RRA:AVERAGE:0.5:30:360") stores 360 rows of 30 steps (300
> seconds = 5 minutes) each.
> If your graph lies entirely in the past 100 seconds, the higher
> resolution RRA will be used.  If your graph starts more than 100
> seconds ago, the lower resolution RRA will be used.
>> There are two RRAs each with different average values (even though there
>> is nothing to average for the later one). Now I wan't to create a graph
>> showing both RRAs.
> As explained above, the first RRA contains the last 360*5 min = 1800
> min = 30hrs of data and the second RRA contains the last 100 seconds,
> it doesn't make sense to graph this data on the same chart (what would
> the x-axis be?).  If you're looking to graph today's data compared
> with yesterday's data, you want to look at this:
>  http://www.vandenbogaerdt.nl/rrdtool/shift.php
> -Sam

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