Re: HD head unloads (was: Re: AHCI power saving)

Jan Engelhardt
2006-11-14T09:41:51Z

On Nov 14 2006 01:43, Henrique de Moraes Holschuh wrote:
>On Mon, 13 Nov 2006, Pavel Machek wrote:
>>On Mon 2006-11-13 12:58:10, Mark Lord wrote:
>>>Jeff Garzik wrote:
>>>>Andi Kleen wrote:
>>>>
>>>>>How does it shorten its life?
>>>>
>>>>Parks your hard drive heads many thousands of times more often than it
>>>>does without the aggressive PM features.
>>>
>>>Spinning-down would definitely shorten the drive lifespan. Does
>>>it do that?
>>
>>Not on my machine.
>
>Heck, given just how much a ThinkPad T43 BIOS will attempt to do it for you,
>consider yourself lucky if the X60 behaves differently. When I thought of
>monitoring the head unload counter through SMART on mine, my HD was already
>beyond 14k unloads... and the notebook had been powered up less than 100
>times :p

Let me jump in here. Short info: Toshiba MK2003GAH 1.8" 20GB
PATA harddisk, in a Sony Vaio U3 (x86, gray-blue PhoenixBIOS).
If idle for more than 5 secs, unloads. Even when not inside any OS,
which really sets me off.
So I wrote a quick workaround hack for Linux, http://tinyurl.com/y3qs6g
It reads a predefined amount of bytes (just as much to not cause
slowdown yet still cause it to not unload) from the disk at fixed
intervals.

>The BIOS likes to set the drive APM mode to something other than "off", and
>in many drives (well, Hitachi ones at least), that means the drive will be
>happy to unload heads every chance it gets, so as to be able to power off
>the head assembly motion drive.
>
>> > Parking heads is more like just doing some extra (long) seeks.
>
>Long seeks don't lift the head assembly off the plates, head unloads do.
>And head unloads will also power down some stuff in laptop HDs, seeks don't
>do that either.

Parking heads is worse than a seek - it takes more time to reload it
than to seek to the other side.

>And even old-style parking places the heads on a different surface than the
>data area. That's a lot different from seeks no matter how one looks at it.
>
>> > Is this documented somewhere as being a life-shortening action?
>
>Yes, although not often with that many words.
>
>For example, a Hitachi Travelstar 5k100 is rated for 600k load/unload
>cycles, and 20k emergency load/unload cycles (each emergency unload counts
>as 30 normal unloads, but the tech docs say it is about 100 times more
>stressfull to the drive). It is in the public drive datasheet, along with
>other important information, such as that the drive needs to spin down often
>(no less than once every 48h) or its lifespan will be shortened.
>
>A typical desktop HD can probably survive a lot less head load/unload
>cycles and spin up/down cycles than that.
>
>--
> "One disk to rule them all, One disk to find them. One disk to bring
> them all and in the darkness grind them. In the Land of Redmond
> where the shadows lie." -- The Silicon Valley Tarot
> Henrique Holschuh
>-

-`J'
--