[nzlug] Fans?!?

[Nevyn]

I've recently upgraded my file server and added another 2 hard drives
(1.2TB Baby!!!).

Anyway, I noticed that the hard drives were all running a tad hot so
loaded up hddtemp and had a look. Yep, sure enough they're running
overly hot. Not a problem says I and I chuck in a great big fan (12cm
diameter) which cooled the hard drives down back to safe limits (by as
much as 15 degree's).

Unfortunately the fileserver is in my room, and a 12cm fan is just way
too noisy.

Fortunately for me it looks like I can put a case fan into my machine
that's monitored. I.e. it's able to show me the RPM's (not the package
system) and that sort of stuff.

So my question(s) to the list are:
1. Is there a special type of fan needed for this sort of thing? (I.e.
can I not just put a plug on the end of the 12cm fan and plug it in?
2. Are there any applications in linux (command line only) that
control the systetm fan?

What I'm thinking of doing is running a shell script that monitors the
temperature on all the drives. If the average temperature gets to 55
degree's, switch on the fan. If the average temperature drops down to
50 degree's, turn the fan off again.

This would hopefully give me enough time to get to sleep rather than
being kept awake by the sound of the damn thing all night and save
some power as well.