linux-kernel - Re: Disk spin down issue on shut down/suspend to disk

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Date:	Tue, 07 Aug 2007 22:26:46 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Tejun Heo <htejun@...il.com>,
	Michael Sedkowski <sedmich@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: Disk spin down issue on shut down/suspend to disk

Henrique de Moraes Holschuh wrote:
> On Tue, 07 Aug 2007, Robert Hancock wrote:
>>> You *do* have to worry about it in any box you turn off daily.  Desktop
>>> HDs will croak fast in that scenario, laptop HDs less so, but still too
>>> fast.  A very good laptop HD can last about 20k emergency unloads (this
>>> is a unit that can do about 600k normal unloads in its lifetime).
>>> Desktop and server HDs don't even come close to those numbers, last time
>>> I checked.
>> It only matters on hard drives which actually use load-unload heads. Lots
>> of desktop/server drives (perhaps some laptop ones as well) still use
>> contact start/stop, which doesn't remove the heads from the platters on
> 
> I am not so sure about that.
> 
> Please correct me if I am wrong, but contact stop in an emergency retract
> shakes the head assembly badly as well. It subjects the head assembly to
> higher acceleration than a normal seek, and a nasty impulse at impact with
> the stopper.  And I very much doubt it is nice to the heads to slide into
> the parking zone at high speed and hit the bumper while over it.
> 
> Unless I missed something, I don't why an emergency retract would not be as
> big a problem as an emergency unload.
> 
> Maybe we should hunt down some proper datasheets for drives lacking head
> load/unload technology, and check what they say about emergency unloads...

I did a bit of a look and didn't find any mention of the subject for 
drives using contact start/stop. I did find mention that the unload 
torque needed is quite a bit higher on load/unload systems, so I would 
imagine that having to extract or store that energy for emergency 
unloads would be more of a demanding task and might be a rougher process.

Just judging from the sound, though, hard power-offs on a desktop 
Seagate Barracuda 7200.10, for example, which is contact start/stop, 
don't really sound any different from a commanded standby. On the laptop 
drives I've seen you can really tell the difference.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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