[mrtg] Re: RRDTool VS MRTG?

Jay Hennigan jay at west.net
Thu Aug 10 18:23:42 MEST 2000

On Thu, 10 Aug 2000, Jack Barnett wrote:

> I have setup an OpenBSD 2.6 i386 computer to act as a router and was going
> to install mrtg to monitor all aspects (cpu, bandwidth, memory, etc) of it
> (already use mrtg to monitor livingston portmasteres/routes and cisco
> routers) and seen a link to RRDTool.
> My question is, what advantages does RRDTool
> (http://ee-staff.ethz.ch/~oetiker/webtools/rrdtool/) have over MRTG
> (http://ee-staff.ethz.ch/~oetiker/webtools/mrtg/mrtg.html) when monitor a
> router/computer.  The OpenBSD router was going to run an snmpd so MRTG could
> get the values.  I want to monitor all aspects of the system that is
> possiable.
> Is RRDTool a rewrite of MRTG? 

It's a rewrite of a portion of it.  "Classic" MRTG has some limitations 
in terms of scalability and flexibility.  As it was originally designed to
count bits (or bytes) passing through an interface in two directions, it
doesn't like values less than 0, non-integer values, negative numbers,
or plotting a number of variables other then 2.  Thus, using it for things
such as plotting temperature can get tricky.  Also, classic MRTG draws a 
new graph every interval, five minutes by default.  This can impact server
performance if there are many inputs. 

RRDTool (Round Robin Database Tool) allows for more flexibility in the
type of data being plotted, and also doesn't create the actual graphs 
until they are requested by a web page "hit".  This overcomes the limitations
of MRTG for plotting oddball or multiple values, etc.  It is also more 
server-friendly in terms of CPU usage provided that your graphs don't 
become the Slashdot feature site and you wind up with an enormous number
of hits.  

> Is MRTG going to get dropped?

No.  MRTG works with RRDTool.  The functionality of MRTG that calls
the SNMP MIBs of the router and extracts the data is still needed in
addition to RRDTool.  There's another piece called "14all" that acts
as glue-ware to fit it all together.  

If you've got plenty of horsepower, and/or just a few interfaces to
monitor, then you might be better off using classic MRTG and skip 
RRDTool.  If you want scalability to hundreds of interfaces and/or 
need to plot non-integer, multiple, or negative values, then use
the combination MRTG-14all-RRDTool.  

Jay Hennigan  -  Network Administration  -  jay at west.net 
NetLojix Communications, Inc.  NASDAQ: NETX  -  http://www.netlojix.com/
WestNet:  Connecting you to the planet.  805 884-6323 

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