On Tue, 20 Aug 2013, Philipp Herz - Profihost AG wrote:
> But I noticed some "strange" behavior when I shutdown a machine. As
> Icinga can not get any values from remote nrpe daemon while remote
> system is down, it's status changed from OK to UNKNOWN (without perfdata).
>
> Up to the point when the remote system is powered on again the graph is ok.
>
> Now, when Icinga is able get "new" performance data from remote system,
> it draws huge peaks of values the hardware does not even support.
This is an intrinsic problem with RRDtool and the way it deals
with counters -- more specifically the way it deals with counters
when they "wrap" (i.e. normally cycle back to zero after overflowing).
In a perfect world, one can deduce a correct *rate* from a mono-
tonically-increasing counter even if that counter occasionally wraps
back to zero by taking the last known value (before the wrap) and the
new one (after the wrap) and summing the before-wrap and wrap-point
delta and the new value. This yields no problems in the data.
However, we don't live in a perfect world, and occasionally counters
get forcefully reset to zero when they otherwise would not have. This
causes RRD to mistakenly apply the "wrap" logic and produce erroneous
results.
Tobi goes to some length to outline coping strategies for these
contingencies in the RRD documentation, including laying out what
values are acceptable when data are written into the RRD and ways
to remove obviously errant data from graphs when producing them, but
those facilities may not be available in the pnp4nagios (and other)
tools in common use.
In short, this is not an Icinga problem, it's an RRD problem and,
depending on the actual tool and implementation you're working with
you may have a large hill to climb to "solve" your issue. The easy
way is to use LIMIT values when producing the graphs to cause impossible
values to become "unknown" and to not get graphed; the trick is picking
the "right" value that'll work for everything.
Cheers!
+------------------------------------------------+---------------------+
| Carl Richard Friend (UNIX Sysadmin) | West Boylston |
| Minicomputer Collector / Enthusiast | Massachusetts, USA |
| mailto:crfri...@rcn.com +---------------------+
| http://users.rcn.com/crfriend/museum | ICBM: 42:22N 71:47W |
+------------------------------------------------+---------------------+
------------------------------------------------------------------------------
Introducing Performance Central, a new site from SourceForge and
AppDynamics. Performance Central is your source for news, insights,
analysis and resources for efficient Application Performance Management.
Visit us today!
http://pubads.g.doubleclick.net/gampad/clk?id=48897511&iu=/4140/ostg.clktrk
_______________________________________________
icinga-users mailing list
icinga-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/icinga-users
