[rrd-users] how correctly make speed graphics

Steve Shipway s.shipway at auckland.ac.nz
Tue May 24 00:41:05 CEST 2011

> > The problem moose has is that he is plotting the data counter, not a
> > rate derived from it.
> >
> I did not understand you, Could you tell me what to do?

The SNMP traffic you are storing is a continuously increasing counter of the data transmitted; however, you are interested in the RATE (IE, bytes per second).

RRD files have various data types -- gauge, absolute, counter, derive etc.  You have defined your RRD with the wrong data type for your DS.

Say you retrieve value v0 at time t0, and value v1 at time t1.

GAUGE : this is for something you want to plot as-is; eg, the temperature of your device.  At time t1, you store v1.
COUNTER : this is for a constantly increasing value where you are interested in the RATE of change.  At time t1, you store ([v1 - v0]/[t1 - t0]).  I believe it also takes account of 16bit and 64bit counter wrapping.  This is the one you want in this case.  
DERIVE : This is like COUNTER, except that it allows the value to decrease (IE, a negative rate)
ABSOLUTE : This is like COUNTER except that it assumes the value is reset on reading; IE you store (v1/[t1 - t0])

Hope this makes more sense.


Steve Shipway
ITS Unix Services Design Lead
University of Auckland, New Zealand
Floor 1, 58 Symonds Street, Auckland
Phone: +64 (0)9 3737599 ext 86487
DDI: +64 (0)9 924 6487
Mobile: +64 (0)21 753 189
Email: s.shipway at auckland.ac.nz
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