[rrd-users] Re: Adding a new ds to an existing rrd

[Marc Haber]

On Fri, Aug 19, 2005 at 01:57:10PM +0200, Alex van den Bogaerdt wrote:
> On Fri, Aug 19, 2005 at 11:22:50AM +0200, Marc Haber wrote:
> > I need to add a ds to an existing rrd, and would like doing so without
> > losing all history data for the other ds's in the rrd file. This seems
> > to be harder than I expected.
> 
> > Again, the output of rrdtool dump shows that rrdtool is able to print
> > every data point available automatically, but the XML format is hard
> > to parse. It would be so nice to get all data points in the same
> > format as rrdtool fetch prints (or RRDs fetch puts into perl data
> > structures)
> 
> There is another command, rrdtool restore, which reads an XML file.
> 
> The process would be like this:
> 
> -1-  dump the database
> -2-  edit the XML file, alter the header
> -3-  edit the XML file, insert new DS
> -4-  restore the database
> 
> You can do this yourself, or use one of the many scripts available
> on the web.

I was hoping to spare myself the work to learn how to use xslt.

> > Am I missing something, or is rrdtool really missing these useful
> > features?
> 
> This doesn't happen that often.  Many people don't need to add (or
> remove) a DS.  It's not that often that a third direction is added
> to an ethernet card, usually "in" and "out" are enough.  When you
> add an ethernet card to a computer, just use an extra rrd file.

Well, if you think that rrdtool is only useful to plot in/out for
ethernet interfaces, you are using like 2 % of what rrdtool can do. In
fact, even something as simple as an ethernet card gives much more
more data then just input/output octets.

> Maybe you are asking the wrong question and maybe you don't need
> to add a ds to a rrd file.  Maybe you just want to collect more
> data and are looking for a way to store that data ?

I have been using the Debian packages for rrfw/torrus since they first
became available in the experimental distribution. One of the
preliminary versions I have been using productivly didn't properly
create the DS for ifInDiscards, while the current version properly
reads the value from the Interface and tries to write it to the rrd,
which of course fails.

So, I want to add the DS for ifInDiscards so that this value can be
collected in the future. And since I would like to keep the history of
the values already collected, I need to add that DS without losing the
present data.

I hope this all makes sense.

Greetings
Marc

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