On Tue, 24 Jan 2006, Francois Barre wrote:

So my (real) question would be :
- how much a drive consumes ? how long can it be on diet ?
and, on top of this :

Is it possible to make the drives turn slower ? To make the heads move 
slower ? That would be my dream. No more heat, a 10mA consumption, no 
more noise...

Some manufacturers do produce documentation regarding this:

http://www.hitachigst.com/tech/techlib.nsf/products/Deskstar_7K250

It is the "Specification - OEM" document[s] that are interesting, in my 
case lately: "Deskstar 7K250 Specification v1.6 (Serial ATA)"

On page 27 you have "Table 21: Power supply of current models" where you 
can read the power consumption of a drive during various kinds of load 
(startup, idle, random r/w, sleep).

Here you also can see that the "Silent" mode makes the drive use 8.5W 
instead of 10.6W under "Random R/W Average" load. Not that I know how to 
activate "Silent" mode from Linux, but I expect the document to tell you 
what bits you should send over the cable.

I suspect other manufacturers have similar documents, but I don't know if 
they are public or how to find them. Some pointing and clicking on 
websites will probably tell you what you need for your drives.

/Mattias Wadenstein