Data Difference

[friskd]

Looking to create a graph of the difference between two interfaces. We have our traffic out to the Internet graphed, and we have our student traffic portion of that traffic graphed. I would love to graph the total traffic (green) minus student traffic (red) resulting in the admin base traffic.

Currently have two line graphs, so we know the margin between lines is admin traffic, but would love to have that margin be the data for the single total graph.

Any ideas or help on how to do that would be appreciated!

Thanks!
D

[michaelwjoyner]

you want to just graph the ADMIN traffic and not graph the TOTAL and STUDENT?

[friskd]

Correct. But I can't find how or where to do simple subtraction of two data sets to graph that difference...

[gandalf]

Please use a CDEF. Find help at http://docs.cacti.net/manual:087:6_refe ... cdef#cdefs
Reinhard

[michaelwjoyner]

In CDEF's you can create user defined functions

Its located:

Graph Management > CDEFS


There is a sample function in there A+B. You might check how that is made. It looks rather simple.

I am guessing and I apologize if I am mistaken, but I think that you would create a CDEF for A-B or B-A and use your new CDEF in your graph template.

I will monitor this thread, I am anxious to see if I am right.

[michaelwjoyner]

same time. HEHE


I guess I was right. You might want to take a look at the CDEF sample.

Cheers

[friskd]

Thanks all!

Looks as if the CDEF stuff worked... took a bit to tweak it, but it first adds input 2 and 3 (student traffic primary and failover (something + heartbeat ) ) then subtracts that total from input 1. I had to create a 4th data source (with no datasource associated) to do the final bytes to bits CDEF, but yea...

As I suspected, there is SOME traffic on the Student graph that is not Internet bound (as reflected in the graph as negative traffic), but this give me the rough data we need!

Thanks for your help!
Dave