[148701] in North American Network Operators' Group
Re: Polling Bandwidth as an Aggregate
daemon@ATHENA.MIT.EDU (Steve Clark)
Fri Jan 20 11:00:28 2012
Date: Fri, 20 Jan 2012 10:59:37 -0500
From: Steve Clark <sclark@netwolves.com>
To: Chris Adams <cmadams@hiwaay.net>, NANOG <nanog@nanog.org>
In-Reply-To: <20120120155344.GB13300@hiwaay.net>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 01/20/2012 10:53 AM, Chris Adams wrote:
> Once upon a time, Leo Bicknell<bicknell@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.
>
>> 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.
>
>> 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 suggest reading
http://oss.oetiker.ch/rrdtool/tut/rrd-beginners.en.html
--
Stephen Clark
*NetWolves*
Director of Technology
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark@netwolves.com
http://www.netwolves.com
