[mrtg] Target and its mapping to RRD

Steve Shipway s.shipway at auckland.ac.nz
Tue Jun 28 22:14:01 CEST 2011

>However, I'm running into a few things I can't figure out, namely how the Target[] line maps to RRD.

A Target definition corresponds to a single RRD file.  The two lines (IN and OUT) corresponds to two Data Sources (ds0 and ds1) within that RRD.

>For example, is it possible to query more than a two-value pair? RRD can store multiple DS's, 

No -- MRTG came before RRD, and RRD is an extension of the MRTG data structure.  However, if you are using the Routers2 frontend to MRTG/RRD, then you can define 'userdefined graphs' which combine the datasources from multiple Target definitions, giving what you're after.  Then you can have line graphs or stacked graphs, combining any number of individual Target definitions completely or in part.  See the demo on www.steveshipway.org/software 

>Another thing I can't exactly figure out is what happens with this:
>Target[network]; oid1&oid2:community at hostname+oid3&oid4:community at hostname
>Does that result in two DS's where ds0 contains oid1+oid3 and ds1 contains oid2+oid4 or something else?

Yes (though make sure you have the spaces around the + symbol).  Each component is a 2-part array.

>Is it even possible to use such "complex" Target-lines with RRD as a backend?

Yes, this is perfectly valid.  In fact, you can have even more complex calculations with multiple parts, constants, and even external function calls.  Read the (extensive) documentation of the Target line syntax.


Steve Shipway
University of Auckland ITS
UNIX Systems Design Lead
s.shipway at auckland.ac.nz
Ph: +64 9 373 7599 ext 86487

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