Polling Bandwidth as an Aggregate

Keegan Holley keegan.holley at sungard.com
Fri Jan 20 16:01:25 UTC 2012

2012/1/20 Chris Adams <cmadams at hiwaay.net>

> Once upon a time, Leo Bicknell <bicknell at ufp.org> said:
> > To suggest Netflow is more accurate than rrdtool seems rather strange
> > to me.   It can be as accurate, but is not the way most people
> > deploy it.
> Comparing Netflow to RRDTool is comparing apples to cabinets; one is a
> source of information and one is a way of storing information.

I assumed he meant an RRDTool kit that creates graphs with RRDTool.
Technically, mysql is the "way of storing information".  RRDTool processes
it and has the ability to make it pretty for us humons.

> > RRDTool pulls the SNMP counters from an interface and records them to a
> > file.
> No, RRDTool stores data given to it by a front end such as MRTG,
> Cricket, Cacti, etc.  That front end can fetch data from any number of
> sources, including (but not limited to) SNMP.  RRDTool then stores
> information in its database.

Same as above

> > With no aggregation, and assuming your device has accurate SNMP,
> > this should be 100% accurate.  While you are right that the defaults for
> > RRDTOOL aggregate data (after a day, week, and month, approximately)
> > those aggregates can be disabled keeping the raw data.
> RRDTool does not store the raw data.  Even for 5-minute intervals, it
> adjusts the data vs. the timestamp to fit the desired interval.  Since
> you don't read every counter at the exact time of your interval, RRDTool
> is always manipulating the numbers to fit.  The only numbers that are
> not changed before storing are the timestamp and value for the most
> recent update (which get overwritten at each update); everything else is
> adjusted to fit.
> I think every graphing tool does this.  I pretty much ignored this though
since I was asking about aggregating data from multiple objects not
aggregating data over time.


> --
> Chris Adams <cmadams at hiwaay.net>
> Systems and Network Administrator - HiWAAY Internet Services
> I don't speak for anybody but myself - that's enough trouble.

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