[rrd-users] Re: GPRINT max/average discrapancies

[Alex van den Bogaerdt]

Day Dreamer wrote:

> I just installed MRTG w/ RRDtool and 14all.cgi.  They
> are running but the mininal, maximal, average, and
> current numbers displayed on the bottom of the graphs
> are questionable a bit.

rrdtool script has:
DEF entries:  in,out, min,mout       bytes for average and maximum
CDEF entries: fin,fout, fmin,fout    bits for average and maximum 
CDEF entries: pin,pout               percentage for average only

Plotting:
AREA fin, LINE1 fout                 mrtg compatible averages

Printing:
fmin,pin    Maximal_In         12345.78 M      (123.56%)
fmout,pout  Maximal_Out        12345.78 M      (123.56%)
fin,pin     Average_In:        12345.78 M      (123.56%)
fout,pout   Average_Out:       12345.78 M      (123.56%)
fin,pin     Current_In:        12345.78 M      (123.56%)
fout,pout   Current_Out:       12345.78 M      (123.56%)

> I only have data points for 3 days worth so any
> additional days graphed are NaN or flat line as
> expected.  However, is I graphed this w/ "-s -10day"
> as suppose to "-s -9day" I will get different pin:MAX,
> puut:MAX, and other figures slightly between the
> graphs.  

I looked again and found no "pmin","pmout" which I think
are necessary to print the percentage for the maxima.

> So, how exatly does GPRINT gather the data w/ cf set
> to MAX, AVERAGE, and LAST?  

It seems to me this script is printing the maximum of
the averages.  If you did not already do so, check out my
faq page (http://faq.mrtg.org/) and follow at least the
first to links.  This is where normalization, averaging
etcetera is described. Also see the faq section, 4th link
at configuring.  While this is not exactly the case here
it describes part of the problem.

> In this example, pin is obrtain from DS=ds0:AVERAGE. 
> So, even though I'm performing GPRINT w/cf set to MAX,
> it should still give me the largest data point within
> ds0:AVERAGE, right?  

Only after consolidating.  This will happen when the
image is generated unless the time per pixel corresponds
with a time per row in one of the RRAs.

There can be four problem areas here:
1) mrtg
2) 14all.cgi
3) rrdtool
4) your understanding of averaging et al

I think at least (2) and (4) are the case here.  In both cases
it is *almost* right.  In order to improve (4) you have to do
just a bit more reading and experimenting.  The problem at (2)
can be one of the experiments: copy pin,pout to pmin,pmout and
make the necessary other changes in the script.  See if this at
least solves the incorrect percentages.  If so, you've found a
bug; congratulations :)  (note: the bug would be in the script
or in the program creating it, 14all).

When you've gained a better understanding of, and more experience
with mrtg/14all/rrdtool, I suggest you start checking if you want
to keep using MRTG.  Especially at high rates and/or when you have
special needs for graphing, it may be better to choose another
front end for rrdtool.

HTH
-- 
   __________________________________________________________________
 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
| work                                                         private |
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| http://faq.mrtg.org/                                                 |
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