On my system I had ~400k disk writes every three seconds and this was really starting to annoy me, so today I decided to find out where they came from.

I have now tracked them to the "nVidia GPU Core" sensor in my GKrellM setup. Once I removed that one, the writes stopped.

Does anyone know why either GKrellM or lm_sensors would need to write that much to disk? I thought it was supposed to be a monitor?

No idea I use Gkrellm myself, and lm_sensors runs on bootup, and I've never seen that. I also use an nVidia card, though I don't recall off the top of my head whether my gKrell has a provision for monitoring the AGP card..
My guess would be merely the way 'something' is configured, making it log stuff on an extremely regular basis .
What exactly was the contents of the files/logs being written? What sort of stuff was it saving?

Yes I was thinking that as well, but 400k is a pretty big log file isn't it? Besides, I didn't see any option regarding the log frequency in the gkrellm setup. Does lm_sensors do logs as well?
No idea. Is there any way to find out? I only found out that it was GKrellM by deleting one process at a time until the writing stopped. (And of course since I was looking at GKrellM to notice if the disk writing changed, it was one of the last processes to kill. )

Edit: Just some additional information: there's no log file in the .gkrellm directory, and none of the log files in the /var/log directory have been modified that recently.

Hmm..
Well, I guess the logsize is relative, though I suppose 400k is pretty large to be written every 3 seconds definitely!
I don't know if lm_sensors itself actually logs anything, at least my installation does not, however it's possible though unlikely that maybe the syslog daemon is doing the logging..
Perhaps adding a line like this:
*.* /dev/tty12
to the syslog.conf file *might* give an indication of what's going on every 3 seconds.
To use this addition to syslog, add it to the file, save it, and restart the syslogger daemon. Then CTRL-ALT-F12 to see tty12 where everything syslog catches will be logged to the screen.
It might help identify what's doing what.

As to finding out what's being saved to what file, of course it will help to know where to locate the file first. But a place to start would be /var/log/ or /var/adm/.

Well, nothing changes in the /var/log/ directory. /var/adm/ doesn't exist on my system. Also syslog is not involved, because it was one of the first processes I killed, and the disk writing continued.

To try and locate the file that is written, I activated the sensor again, let it write a couple of times, and then ran but apparently nothing was created or modified at that time even though that was the time when the sensor was active...

Interesting, and good try!
I don't know what to suggest, other than *maybe* checking the nVidia Forum at www.nvidia.com or seeing if there's any contact address or developer site for gkrellm where you could pose the question? Maybe indirectly through Sourceforge or wherever gkrellm comes from?

Yes, I'll ask around a bit, perhaps also in the debian forum. Luckily it's not something I can't live without

Thanks a lot for your help and suggestions, I really appreciate it!