[mrtg] Re: RRDTool and scripts

[Alex van den Bogaerdt]

Kerry Kincaid. wrote:

> Since there was about 24 days less data to view that the numbers were much
> smaller than usual.  However, this translated into a spike on the graphs of
> monster proportions.  I gathered from some of the archived messages that the
> Software assumed that the number increased to maxbytes then rolled over to
> zero and continued to go up and calculated the value accordingly.   That was
> the wrong thing to do and I'd like to know how I can have it still record
> the data as a counter, but not choke when a log file is deleted.

Proper solution:  front end decides when a wrap occured and when it
did not.  If it did not (so: a reset or so) it sends "U" for unknown
to RRDtool.  Front end in this case is the script that gathers the
values.

Good workaround:
In stead of COUNTER you can use the DERIVE data source type.  When the
minimal tolerable value is set to 0, any wrap or reset will result in
a NaN value generated by the back end.
You can use "rrdtool tune" to alter the DS  *and* the min-value.

cheers,
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