[mrtg] Re: Business Hours and 95%ile.

Jay Hennigan jay at west.net
Thu Sep 6 23:36:53 MEST 2001

On Thu, 6 Sep 2001, Forthofer Russ wrote:

> Jay:
> You are probably right that the "business hours only" is not for everyone.
> I would agree that in using MRTG to look for anomalies in utilization you
> want to look at the whole day.  However, IMHO, there are some cases where it
> can be quite helpful to look only at the business day.  For example, if a
> line is used primarily during business hours, average utilization across a
> 24-hour day is pretty meaningless.  Average utilization and 95th percentile
> utilization across the business day, however, can be useful statistics,
> especially in terms of gathering historical data and tracking growth.  If
> the business day "average" is what is being sought (in my case it is), then
> simply zeroing out the non-business hours does not resolve the issue, as the
> zeroes would skew the average.

There are settings in MRTG to control this behavior.

   Log unknown data as zero instead of the default behaviour of repeating
   the last value seen. Be careful with this, often a flat line in the
   graph is much more obvious than a line at 0.

   Normally we ignore all values which are zero when calculating the
   average transfer rate on a line. If this is not desirable use this option.

It would seem that if you run from cron, set the crontab for the intervals
you want, set "unknaszero" and do NOT set "withzeroes" that your averages as
shown on MRTG will indeed reflect just the business hours.  The graphs will
be zeroed out during non-business hours.

95th percentile is a different story.  It will plot the zeros unless you
hack it, but this probably won't affect the results if the 5% peak timeslots
are within business hours.

Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
WestNet:  Connecting you to the planet.  805 884-6323

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