[collectd] Custom RRAs when creating RRD file

[kgardenia42]

On Tue, Mar 27, 2012 at 11:23 PM, Lindsay Holmwood
<lindsay at holmwood.id.au> wrote:
> 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.

ok.

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

Great.

>
> 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.

I can't seem to figure out what combination of these settings I can
use to get the behaviour I want.

These are the RRAs I want in my RRD:

        RRA:AVERAGE:0.5:1:100
        RRA:AVERAGE:0.5:6:100
        RRA:AVERAGE:0.5:12:50
        RRA:AVERAGE:0.5:120:50
        RRA:AVERAGE:0.5:720:24
        RRA:AVERAGE:0.5:17280:7

Questions:

* each of those RRAs wants a different number of records retained.
100, 100, 50, 50, 24, 7.   Since RRARows seems to be a global setting
which is applied to *all* RRAs I don't see how I have the granular
control to specify different values for each RRA.

For example, in collectd.conf if I were to do:

<Plugin rrdtool>
    DataDir "/var/lib/collectd"
    RRARows 100
</Plugin>

That means I'd have 100 rows for *all* my RRAs created by collectd.
Or am I missing something?  There a way to control this on a per-RRA
rather than a global setting?  The control this config gives doesn't
seem fine grained enough for multiple RRAs or multiple RRDs unless I'm
missing something (which I probably am).

* The manual also says "for each timespan, it calculates how many PDPs
need to be consolidated into one CDP by calculating: number of PDPs =
timespan / (stepsize * rrarows)".  But again, if the RRARows setting
is global then all calculations will be a function of that one
setting.  I guess I could round up all RRARows to the largest value I
want (100).  But then I expect I would have to do a lot of number
juggling to get my numbers to add up to what I want. Is that basically
what you would recommend?

* It is a minor point but the manual says "this plugin creates
RRD-files with three times five RRAs, i. e. five RRAs with the CFs
MIN, AVERAGE, and MAX".  Since I only want AVERAGE is there any way to
specify that I don't want the others?

Thanks for your help.