[rrd-users] Re: RRDTool Design Considerations

[Carlson Peters]

Jason Frisvold wrote:
> 
> Greetings,
> 
>         I'm creating a massive system for monitoring all of our
> equipment.  This includes graphing everything from traffic to memory
> usage, doing Trend Analysis on the data, 95th percentile calculations,
> and Thresholding.  However, I need some information regarding rrdtool
> that I can't seem to find in the documentation.
> 
>         First off, when I create the RRD's, I have to indicate what ds's
> I want included.  I was considering creating a single RRD for each piece
> of equipment and putting multiple (probably 20+) ds's in each.  How well
> does this scale for performance?  Will the performance be severly
> impacted by creating an RRD with a large number of ds's?

Just from offhand experience, having lots of ds doesn't seem to impact
performance much.  I have several RRD with 20+ ds.  I would even think
that the overhead of opening/rolling up/writing more RRD files would be
much more significant than having more ds in a single file.  This is
especially true if you plan to invoke the CLI for each update.  The Perl
RRDs module scales much better if you have hundreds or thousands of RRD
files to update.

> 
>         Secondly, this needs to be scalable.  So, at points in the
> future, I may need to add ds's to an RRD.  How is this accomplished?  So
> far, the best I can tell is that I need to use rrdinfo to get all the
> current settings, create a new RRD with these settings and the new ones
> added, dump the old RRD to an XML file, and then write a parser to put
> the old info from the XML into the new RRD.  Is there some easier way to
> do this?  Does anyone currently have code that accomplishes this?

Unless I'm absolutely certain, I always add a few extra unused counters
and gauges to my RRD up front.  It makes it so much easier to expand
later.  Some people have written scripts to dump the data, recreate the
RRD with more RRD, and insert it again.  This is another alternative.

> 
>         And lastly, when using rrdfetch, is there any way to specify
> which ds values to return or will it always return all of them?  Are
> there plans to change this?

If you are using the RRDs module, it's pretty easy to slice out the
pieces of the row you are interested in.

> 
> Thanks in advance for the info....
> 
> ---------------------------
> Jason H. Frisvold
> Senior ATM Engineer
> Engineering Dept.
> Penteledata
> CCNA Certified - CSCO10151622
> friz at corp.ptd.net
> ---------------------------
> "I love deadlines.  I especially like the whooshing sound they make as
> they go flying by." -- Douglas Adams [1952-2001]
> 
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-- 
Carlson Peters
Applications and Services
Qwest IP Applications/Network Engineering
(303) 226-6681 Work
carlson.peters at qwest.com

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