[rrd-users] Re: Manipulating and Graphing Data

[Tony Varriale]

Hi...thanks for the info.  I did try DERIVE but I get very inaccurate results.

For example:
I had about 400 drops in the queue that were generated.  The graphs and data were showing anywhere from 8-16 drops.  I again verified the actual data with a manual snmpwalk.

When I have DS type set to GAUGE, the data is very accurate (probably <5% off) but I am unable to get the difference between the current value and the previous.  The graph, obviously, keeps expanding on the y-axis.

So, with DERIVE, I am assuming rrdtool takes the value (400) and divides it by the update rate specified when creating the rrd (300 seconds).

Any ideas on how to solve this?

Also, maybe I misunderstood the documentation but this is what I have previously read: "The original value you have supplied is stored as well and is also taken into account when interpolating the next log entry."  Is this not true?

Thanks!

tv
----- Original Message ----- 
From: "Alex van den Bogaerdt" <alex at ergens.op.het.net>
To: <rrd-users at list.ee.ethz.ch>
Sent: Monday, October 30, 2006 6:08 PM
Subject: [rrd-users] Re: Manipulating and Graphing Data


> On Mon, Oct 30, 2006 at 05:45:44PM -0600, Tony Varriale wrote:
> 
>> I am currently polling a qos drop queue and it returns the correct value. 
>> The values are getting stored correct and everything looks great.
> 
> No, they ("the values") are not stored.
> 
> This wrong assumption is probably the foundation of the rest of your
> work, so all is flawed.
> 
> You don't store numbers in an RRD.  Rates are stored, and they are
> not the ones you put in.  See my site, see the tutorials, see the
> documentation.
> 
>> GPRINT:a:MAX:"Max\:%8.2lf%s" What I would like to graph as "current" is the 
>> (current value - the previous value) in the RRA. This will give me the 
>> amount of change since the last interval.  I assumed I could do this via a 
>> CDEF but I am not sure how to get the previous value to do the subtraction.
> 
> For this, RRDtool has the "DERIVE" counter type.
> 
> -- 
> Alex van den Bogaerdt
> http://www.vandenbogaerdt.nl/rrdtool/
> 
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