[rrd-users] Additional "Unknown"-Value

Tobias Oetiker tobi at oetiker.ch
Wed Jun 10 14:02:36 CEST 2009

Hi n1LL3,

Today n1LL3 wrote:

> oetiker wrote:
> >
> > My sugestion would be that you set your mrhb to only a bit more
> > than your sampleing interval ... (as it should be) now, when you
> > miss samples, or you log 'U' rrdtool will turn the stored data into
> > NaN aka Unknown which will cause the graph to 'disapear' ...
> >
> > My phanstasy is that you want to see the graph break for intervals
> > shorter than your step size ?
> >
> > cheers
> > tobi
> >
> Hello Tobi,
> good idea! At first we want to solve our problem like this as well, but then
> other problems will occure.
> For various reasons it could be that the RRD can not be updated in
> continuous time intervals, for e.g.:
> - system-latency
> - network-latency
> - reload of the monitoring tool
> - restart of the server
> ...
> For that time we have no data for the RRD, but we want to handle it like "in
> dubio pro reo" ("in doubt for the accused"). In this case it would be nice
> if we could have the ability to set the mrbh such high that only very long
> timeperiods (longer than one day) will not be bridged.
> But if there will be a real problem while monitoring something (performance
> data could not be determined for example due to timeout), it would be good
> to have the option to tell RRDtools that it was determined an
> unknown-status.
> This breakdown will be displayed in the graph as well without overwriting
> the breaks by aggregation or additional filling of the graph by using a
> small heartbeat.
> Otherwise it could be fatal, because we want to create service level
> agreements.
> Without this function the SLAs will have wrong results.
> Maybe this could also be very interesting for other monitoring tools.
> I hope you can comprehend what I mean.

yes ... and if component C or D break you would want to have
different states for this too, so that the user can see what the
exact cause of the break was ... I'm afraid you will have to store
this kind of information outside rrdtool ... as rrdtool is not
realy siuted to store arbitrary information from the way it is
designed ...

fact is, you have no data for the given periode, hence you can not
charge your customers for it ... in dubio pro customer ... for
billing purposes I would set 'unknown' to 'zero' then you are on
the safe side, and you have a good incentive to make sure your
monitoring is rock solid ....


> Thanks!

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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