[mrtg] Re: making MRTG faster

[Steve Shipway]

> Hi, our ISP has been using MRTG for a while (still at 2.13.2), great
> stuff, thank you! Our userbase counts a little over 1200,  that's 1200
> HTML pages and 4800 PNG files to take care of. The problem is that the
> pretty powerfull Dell PowerEdge (dual Xeon) is taking almost 
> 50 seconds of full CPU time to finish drawing the graphs every 5
minutes.

The way to speed it up is to move to RRDTool.  This makes a huge, huge
speed gain.  You still use MRTG to collect the data, it is just stored
in the .rrd files instead of in .log files (and you can convert the .log
files to .rrd to preserve your history).  Of course you then need a cgi
frontend such as routers2.cgi (or mrtg-rrd, or 14all) to display the
data ,and the .png files are only generated when required.  Further
speed gains can then be obtained by using mod_perl or speedycgi.  You
also get extra reporting capability when using RRD files.

You can get more performance by getting very fast disks.  MRTG
bottlenecks on disk IO, so the fastest disk and controller you can get
is advised.  Also, if you are using UNIX, then mount the data filesystem
with the noatime option, add extra directory indexing, and use subdirs
for your .rrd files to save MRTG from having to search big directory
indexes.

Adding more memory can help to a point (due to directory caching and
being able to hold multiple threads of perl at once) but disk IO is the
key.

We have a dual 2.5GHz Xeon server that can cope with (currently) 6885
targets, and still have capacity for more.  We have a fast Adaptec
controller with some speedy external SCSI disks (sorry, cant remember
the spec offhand)

Steve

--
Steve Shipway
ITSS, University of Auckland 
(09) 3737 599 x 86487
s.shipway at auckland.ac.nz

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