[collectd] Performance of the rrdtool plugin

[Florian Forster]

Hi Richárd,

On Fri, Sep 19, 2008 at 11:12:14AM +0200, Kun Richárd wrote:
> I use rrdtol plugin, their config is [0], the number of RRD files is 1433.

> I've been watching the iostat and sar statistics, and I seen 2Mb/s
> continuous writing, when the collectd runs.

so you're doing / trying to do either 143 (10 second interval) or 71 (20
second interval) updates per second. In my experience this is about as
much as you can get to disk with the random writes librrd performs. The
transfer rate is also in the range I'd expect.

Fortunately for you, all your RRD files will fit into memory, so you
should be able to gain some performance by telling the operating system
to keep writes in memory for a while. Details on operating system and
file system tuning can be found in the RRDTool wiki at
<http://oss.oetiker.ch/rrdtool-trac/wiki/TuningRRD>.
Especially mounting with the `noatime' and `nodiratime' options has
proven to be easy and effective.

If those measures don't suffice, you can check out the rrdtool plugin's
own performance features. As Alessandro has pointed out, setting
`CacheTimeout' to a minute or two can greatly reduce the IO load on your
system. The entire concept of collectd's rrdtool plugin is explained in
great detail in the ``Inside the rrdtool plugin'' article:
<http://collectd.org/documentation/inside_rrdtool.shtml>

Regards,
-octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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