[collectd] Custom RRAs when creating RRD file

[Lindsay Holmwood]

Hi there,

On 28 March 2012 04:09, kgardenia42 <kgardenia42 at googlemail.com> wrote:
>
> What this does not give me is the RRAs I historically had.  To get
> those I tried messing around with RRARows, RRATimespan etc in the
> <Plugin rrdtool> definition.  This seems to be roughly what I want (in
> that adding new RRARows entries seems to add new RRAs to the resulting
> RRD file) but no matter what I try I can't get it to make a RRD file
> with he same "buckets" as the original RRD (see above).  Am I on the
> right track with RRARows, RRATimespan etc?

Yep, this is the right way to solve that problem.

> Is the granularity of
> control even there to do what I'm trying to do (using RRARows,
> RRATimespan)?

Yes.

> Another approach I tried was to manually create the RRD myself (using
> rrdtool create) and then try to update it with PUTVAL.  However, this
> did not appear to do the right thing.  Should I have expected that
> approach to work?

Not really. The rrdtool plugin would likely have freaked out that the
RRAs in the file didn't match its configuration.

> Would I have more control of how the RRAs are created in the RRD if I
> were to write my plugin in perl or C rather than using PUTVAL from a
> shell script?

In simple terms, collectd has two types of plugins - readers and
writers. Collectd treats the data from all reader plugins the same
way, regardless of what language the plugin is written in.

The read data is passed to a writer plugin, which in this case is the
RRDtool plugin. It's up to each writer plugin to decide how it stores
its data, downsampling it or otherwise.

In your case, the RRDtool plugin handles writing the data to the RRD
files based on the setting supplied in your collectd configuration, or
by using the defaults.

My recommendation is to keep plugging away at getting the RRA*
settings right. The rrdtool plugin documentation in the man page
provides a good primer of all the settings you'll need:

  http://collectd.org/documentation/manpages/collectd.conf.5.shtml#plugin_rrdtool

Specifically, you'll need to set RRARows, RRATimespan, XFF.

Let me know if you need any further help!

Lindsay

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