[drraw-users] Begginer question: how to combine two rrd files?

[David Nolan]

On 10/3/06, Tony T. <rollthebones at gmail.com> wrote:
> Hi all,
>
> I am using Drraw 2.1.3 to create graphs from data that is collected for Orca
> use on Solaris systems. Orca is good at it's own graphs but sometimes its
> nice to get on the fly output as well. Usually I can get simple graphs but I
> am at the point now where I need to do some math on the RRDs.
>
> I have not been succesful in combining output from RRD files to give me a
> SUM, i.e. one RRD is cpu_usr, the other is cpu_system.  To get the total
> utilization I need to add these two together but I can't figure out how to
> do it.  Everything I have tried in the CDEF sections has failed, probably
> because I am at a loss as to what needs to go where.
>
> Can anyone help me?
>

CDEF fields take an RPN expression, i.e.   in this case you want
something like a,b,+
where a & b are the value identifiers you see in the Name Seq column in drraw.

Ultimately, drraw is just providing an interface for sending arguments
to rrdtool, so you probably need to read the documentation of rrdtool
to fully understand what you can do in a CDEF.  Specifically read the
'rrdgraph_data' man page.

-David