Disk access just before shutdown power off.

Disk access just before shutdown power off.

[James Courtier-Dutton]

Hi,

When I shutdown my Linux laptop, it does an orderly shutdown with quite
a lot of HD activity during shutdown which eventually stops when the
screen goes blank. Then there is some delay (5-10 seconds) and then a
quick flurry of HD access just before it powers itself off.
Why is this last bit of HD access needed?
Surely, if the system is shut down enough to not use the screen any
more, why does it need the HD?
I am asking, because it would be nice to disable this need of the HD
just before it powers itself off. This would allow me to lift up the
laptop just a bit earlier and place it in my backpack when the screen
blanks without having to worry about HD failure due to shock.
I think it would be nicer if the HD would shut itself down just before
the screen goes blank.

Kind Regards

James

Re: Disk access just before shutdown power off.

[Robert Hancock]

On 07/20/2009 07:34 AM, James Courtier-Dutton wrote:
> Hi,
>
> When I shutdown my Linux laptop, it does an orderly shutdown with quite
> a lot of HD activity during shutdown which eventually stops when the
> screen goes blank. Then there is some delay (5-10 seconds) and then a
> quick flurry of HD access just before it powers itself off.
> Why is this last bit of HD access needed?
> Surely, if the system is shut down enough to not use the screen any
> more, why does it need the HD?
> I am asking, because it would be nice to disable this need of the HD
> just before it powers itself off. This would allow me to lift up the
> laptop just a bit earlier and place it in my backpack when the screen
> blanks without having to worry about HD failure due to shock.
> I think it would be nicer if the HD would shut itself down just before
> the screen goes blank.

It's not clear exactly what point in the shutdown process the screen 
going blank corresponds to. Do you have the kernel output going to the 
console during the shutdown process? If not, enabling that might be 
useful to tell what's going on.

The last thing the kernel does with the disk before power-off is flush 
the cache and tell it to go into standby mode. It seems like some disks 
are dumb enough to spin up as a result even if there's nothing to flush 
and it was already spun down. Also, in some cases the BIOS decides to 
issue its own such commands after the OS tells it to power down, which 
can have similar results. I believe there's a blacklist of system models 
that are set to skip the kernel standby issuing to avoid the double 
spin-down.

Re: Disk access just before shutdown power off.

[Jon Masters]

On Mon, 2009-07-20 at 14:34 +0100, James Courtier-Dutton wrote:

> When I shutdown my Linux laptop, it does an orderly shutdown with quite
> a lot of HD activity during shutdown which eventually stops when the
> screen goes blank. Then there is some delay (5-10 seconds) and then a
> quick flurry of HD access just before it powers itself off.

That would be the journal being synced back to disk as an fsync is done
prior to unmounting/remounting-ro. You can't do anything about this
because it needs to be the last thing that is done.

Jon.

Re: Disk access just before shutdown power off.

[Denys Vlasenko]

On Mon, Jul 20, 2009 at 3:34 PM, James
Courtier-Dutton<James@superbug.demon.co.uk> wrote:
> When I shutdown my Linux laptop, it does an orderly shutdown with quite
> a lot of HD activity during shutdown which eventually stops when the
> screen goes blank. Then there is some delay (5-10 seconds) and then a
> quick flurry of HD access just before it powers itself off.

Either your BIOS does something very weird with your disk
when OS commands it to power off (unlikely),

or your system is set up in a way where there is no visible
output when X is killed, but the system (Linux) is still
running (shutting itself down).

Some distributions get fancy ideas about "not scaring users
with this text output scrolling up at boot & shutdown".

This has nice side effect of users not noticing any
potentially useful messages at boot or shutdown. :(

--
vda

Re: Disk access just before shutdown power off.

[Maciej Rutecki]

2009/7/20 James Courtier-Dutton <James@superbug.demon.co.uk>:
> Hi,
>
> When I shutdown my Linux laptop, it does an orderly shutdown with quite
> a lot of HD activity during shutdown which eventually stops when the
> screen goes blank. Then there is some delay (5-10 seconds) and then a
> quick flurry of HD access just before it powers itself off.
> Why is this last bit of HD access needed?
> Surely, if the system is shut down enough to not use the screen any
> more, why does it need the HD?
> I am asking, because it would be nice to disable this need of the HD
> just before it powers itself off. This would allow me to lift up the
> laptop just a bit earlier and place it in my backpack when the screen
> blanks without having to worry about HD failure due to shock.
> I think it would be nicer if the HD would shut itself down just before
> the screen goes blank.
>

It's HP/Compaq laptop?

Regards
-- 
Maciej Rutecki
http://www.maciek.unixy.pl