[ltp] [PATCH] 2.6.17: Unload disks heads before powering down

[Henrique de Moraes Holschuh]

On Tue, 26 Sep 2006, Shem Multinymous wrote:

> >The EH suspend subroutine does a STANDBY IMMEDIATE command, and that
> >flushes caches and spins down the disk, which IS the right thing to do on
> >a system shutdown, but quite less so for a system reset.
> 
> Any real drawback to doing an UNLOAD IMMEDIATE instead of STANDBY
> IMMEDIATE?

Is Unload Immediate widely supported?

> >> Any idea where that comes from, and how it relates to the SuSE head
> >> unload patch?
> 
> >If you shutdown the scsi bus, the unload patch will spin down the disk.
> 
> I'm getting a spindown on reboot (i.e., shutdown) even without the SuSE
> patch.

Check the userspace scripts too.  They may be doing it (get rid of hdparm
and userspace won't spin down disks anymore).  Add some printk on libata-eh
(2.6.18) to track down when *_eh_suspend is called...

> devices in order to write the snapshot to disk. Currently this causes a
> disk spin-down and spin-up, which is bad for the disk and bad for suspend
> time.
> 
> >I suspect the "so don't do it" finale for this thought is only possible
> >with 2.6.18,
> 
> What changed here in 2.6.18?  I've tested with vanilla 2.6.18, with
> 2.6.17.4+suspend2-2.2.7.1 and with 2.6.17.13+suspend2-2.2.7.6.

2.6.18 has the new Linus way of doing PM, AFAIK.  Not to mention the
entirely new libata EH path.

> >Suspend2 2.2.8 + kernel 2.6.18 is corrupting the page cache here, do
> >*not* use it if you value your data.
> 
> Does it?! During suspend, you mean? I was just about to test that...

Well, it happened after resume from disk.  I have filled a bug about it
already.  I get absolutely no corruption whatsoever from S3 (without
suspend2 patches).

I have seen suspend2 S3 corruption (I don't recall if there were S4
corruptions as well) with 2.6.17, but it was a silent corruption that
eventually caused ext3 to go berserk.  I don't have a working suspend2
system (S3 or S4) since 2.6.16 days.

-- 
  "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