[rrd-users] rrds on ext2 partition?

nate rrdtool at aphroland.org
Tue Jul 8 03:06:39 CEST 2008

Bernard Li wrote:
> http://www.mail-archive.com/ganglia-developers@lists.sourceforge.net/msg04205.html
> Perhaps this is something we need to do some research on and get a
> better understanding.

It certainly is more difficult to add/remove metrics from within an
existing RRD file, so I guess the trade off is how dynamic is the
environment? How often does someone need to add/remove stuff? For
my monitoring at least I have a standard set of stats I collect for
each type of service. It did take some work to determine what those
stats are best, but now that I've determined that it's extremely
rare that I need to change which stats are collected from a type of
system. When I need to add stats I try to find a bunch of new stats
to add and put them in a new file. When I don't need to use stats
that are being collected anymore I just stop using them, even though
they are still being collected.

It is possible, I believe to add/remove data points from an RRD,
I believe it involves exporting the file to XML and re-importing it
to the binary format. For developers of a monitoring application it
shouldn't be too hard to implement I think.

Another method would be to name the data sources in the RRDS to be
generic names, and you can pre-populate an RRD with say 10 or 20 or
30 data sources, and configure the monitoring app to map those
generic names to the kind of stats that you want. When your not
using those data sources, I think they still need to be updated but
you can populate them with the "U" value (for unknown).

Note that my cacti installation is highly custom. The default cacti
behavior is pretty dumb too in that it doesn't consolidate data points.
The previous cacti installation that I inherited with my new job
struggled to update about 5000 data points in a 5 minute interval,
and as a result dropped tons of data as it couldn't update the
files fast enough. As mentioned before the newer system collects
more data, at 1 minute intervals and does so in a fraction of the

I've spent easily a couple hundred hours customizing cacti and have
a pretty good system in place, though cacti really wasn't designed
with consolidated data points in mind so there's a lot of manual
labor involved with setting up a new system. As with everything
there's a trade off..for me right now it's worth it.


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