Yup, I agree now that active cooling is the norm for these
drives...thanks to everyone here for the education on that point.
But, are we sure the motor is the primary source of heat in these
drives?
It is definitely one source, though others include the
friction of platters spinning at thousands of RPM, the
actuator coil, and the active electronics on the circuit
board.
The amount of energy required to keep the platters spinning
at constant rotational velocity, once the target velocity has been
reached, should be minimal.
Depends on your definition of minimal. Certainly it takes
less energy that spinning up from a cold start, but consider
that the motor is 'sunk to the drive frame and it doesn't
take much heat to warm a hunk of metal by 20C.
Changes in speed (e.g. spin up or spin
down) take energy and produce heat -- but physics tells you that once
a platter is at speed, the amount of energy to keep it at that speed
is hardly anything.
You can google for drive power consumptions, which may be
lower than that stated on a label or spec sheet (as those
may be peak current or at least in the drives most active
seeking & I/O state) but are still going to be a few hundred
mA on the 5V & 12V rails. Suppose only 5W total and this is
still enough to heat a drive fame by 20C.
It's just got to overcome gravity and friction.
So, I'd bet that keeping a platter spinning at 7200 RPM consumes
barely measurably more energy than one at 5400 RPM.
Perhaps, but there are too many variables to so easily
conclude this as any given 5K4 RPM drive doesn't necessarily
have all parts in common with a different 7K2 RPM drive.
Some 5K4 RPM drives also warm up a fair amount and it is
prudent to ensure they receive *enough* airflow too.
I thought the main source of heat in these drives was the (ever
denser) packaging of the electronics within them...maybe I'm wrong and
it is the motor...but I can't picture it...
Why would it have to be one or the other instead of both
(producing significant heat)? A drive frame just doesn't
have a large surface area and is smooth like a metal
container for the parts instead of a maximal heatsink area
as on a purpose-designed heatsink. They could make drive
frames with larger heatsink area, but then it would require
a larger mounting bay or smaller platters.
If you took a CPU producing 5W of heat and put a heatsink on
with similar surface area and minimal airflow through it,
that 'sink would also typically rise by more than 10C over
the ambient temp. Power has to go somewhere, you have a
(typically) 300W or larger PSU and though the system might
only use 50-75% of that potential, it's going to turn into
heat among all consumers. We might as well say it would be
nice of a CPU or PSU didn't produce enough heat to need
active or induced-passive airflow, but performance drives
the industry.
As for motor vs electronics, why do we need to know this?
It's not as though you can effectively separate one from the
other and use the drive. Wishing that computer parts used
far less power than they do is a bit futile, unless you're
willing to either pay significantly more for parts optimized
towards power conservation, and/or lower performance. The
industry is typically focused on performance more than power
and cooling requirements, and of course to have a reasonable
reliability while still staying cost-competitive with other
similar products.
Since a typical computer target application includes a case
with rear exhaust fans, and the ideal is to target OEM
sales, the drive manufacturer needs not design all drives
towards least heat, only towards a manageable level of heat
in the target environment. If the system OEM had to choose
between a drive that costs 40% more but produces less heat,
when the system was designed with enough cooling margin to
accomdate the lower priced drive, then when all else is
equal they'd choose the lower cost drive and so these sales
determine which parameter is more important in selling
drives.
