[mrtg] comparison graph creation

[Steve Shipway]

> Right now, I have two graphs and I'd like to combine them into one.
The
> first graph uses SNMP to tell me how many connections I have going to
a
> server via my foundry switch statistics. The second graph uses SNMP to
> tell me the CPU utilization on that same server. 

The problem with this is that you need two separate y-axis scales, and
RRDTool like to have only one.

You can combine the two graphs to one relatively easily, either by using
a userdefined graph in the routers2 frontend, or else by defining a sum
target as Jan Koelstra says.  However, when they display, they will
share a y-axis so is your CPU use is 0-100% and your active connections
is 0-10000 then you will probably have a CPU line that is so small as to
be invisible.

If this is the case, you can do it in routers2 by defining one target as
the CPU, and another target as the connections but with a Factor[] of
0.01.  Then you have to set your LegendI[] labels as 'CPU (percent)' and
'Connections (thousands)' and your YLegend[] as blank.  Probably the
connections Target will also need to have
'routers.cgi*Options[]:fixunit' (to prevent the 'k' prefix) and
'ShortLegend[]:k'.  Define a userdefined graph over the pair using
'routers.cgi*Graph[]:combined noo nototal noaverage' and it should work.
It's a bit of a hack, though.

Steve