IBM Active Protection System Approach

[Stefan Bethke]

Am 22.08.2005 um 17:26 schrieb Søren Schmidt:

> On 22/08/2005, at 10:08, m.ehinger at ltur.de wrote:
>> what would be the best approach to implement aps on FreeBSD?
>>
>> I got an Accelerometer driver which will deliver data. First  
>> Version is available at
>> https://sourceforge.net/project/showfiles.php? 
>> group_id=138242&package_id=160977
>>
>> We have to poll the device for information quiet often to detect a  
>> possible shock early enough to park disk drive heads.
> Urhm, what type of "accidents" is it we want to protect against here ?
>
> It will take several tens of mS to get the heads parked if not  
> hundreds, and the worst case scenario would be that the "accident"  
> will happen just as the heads are on the way to the parking zone  
> which would *really* destroy data on there, unless the disk has  
> special HW to just quickly lift the heads or something.

I have no insight into either IBM's or Apple's implementation, but  
I've read that they both rely on detecting the machine being in  
freefall, or similar acceleration states, as a cue to have the HD  
park the heads before a possible impact.

Early reports from Mac enthusiast sites (and I believe similar  
reports from IBM users) indicate that the hysteresis is so small that  
gently pounding the table the notebook is sitting on will make the  
drive park the heads, and lead to 10 to 20 seconds delay before the  
drive can be accessed again.

Given how tightly coupled mechanically the HD in most notebooks is to  
it's shell, it seems a very good idea to pursue.

If you have access to a new(ish) PowerBook, I recommend checking out  
http://www.kernelthread.com/software/ams/. The sensitivity of the  
accelerometer is truely astounding.  (For those who haven't seen it:  
you turn the notebook, and the demo window is turned so it stays  
level.  It takes *really* small movements to confuse the system.)


Stefan

-- 
Stefan Bethke <stb at lassitu.de>   Fon +49 170 346 0140