Turning Off the Computer

[Ward Vandewege]

On Sat, Oct 18, 2008 at 09:32:17PM -0400, Jarod Wilson wrote:
> On Sat, 2008-10-18 at 21:13 -0400, Bruce Borland wrote:
> > The other night I asked my son to turn off the computer.  He apparently 
> > did not want to wait for the computer to shut down normally, so he 
> > decided to switch off the power to the machine, stopping it immediately. 
> >  I told him that was not good to do, but he asked me why.  I did not 
> > have an answer for him.  He did this to our Windows machine, but I 
> > understand that it is not good to turn off a Linux machine this way 
> > either.  Can someone explain what problems are caused by such an 
> > immediate shutdown?  I would like to know, and would like to tell my 
> > son, too.  Thanks.
> 
> Hard disks are slow, so operating systems tend to cache data into
> volatile system memory, before periodically flushing it out to disk --
> only doing one larger batch write vs. lots of small writes all over the
> place is a performance win. Pulling the machine in mid-flush means the
> on-disk data winds up in an inconsistent state. In some cases, a hard
> drive that looses power while in the middle of writing data can even
> cause physical damage to the disk platters (rare anymore these days
> though). 

That was what the 'disk parking' feature was for. Remember, a long long time
ago, that a drive had to be 'parked' manually before you could cut power to
it? 

Drives have been 'auto-parking' for a long time now (cf
http://www.storagereview.com/guide2000/ref/hdd/op/actParking.html). I
certainly have not seen a drive in the past 15 years or so that needed manual
parking.

Thanks,
Ward.

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