dangerous situation with shutdown process

[Wilko Bulte]

On Thu, Jul 14, 2005 at 12:14:49PM -0700, Kevin Oberman wrote..
> > Date: Thu, 14 Jul 2005 20:38:15 +0200
> > From: Anatoliy Dmytriyev <tolid at plab.ku.dk>
> > Sender: owner-freebsd-stable at freebsd.org
> > 
> > Hello, everybody!
> > 
> > I have found unusual and dangerous situation with shutdown process:
> > I did a copy of 200 GB data on the 870 GB partition (softupdates is 
> > enabled) by cp command.
> > It took a lot of time when I did umount for this partition exactly after 
> > cp, but procedure finished correctly.
> > In case, if I did “shutdown –h(r)”, also exactly after cp, the shutdown 
> > procedure waited for “sync” (umounting of the file system) but sync 
> > process was terminated by  timeout, and fsck checked and did correction 
> > of the file system after boot.
> > 
> > System 5.4-stable, RAM 4GB, processor P-IV 3GHz.
> > 
> > How can I fix it on my system?
> 
> SCSI or ATA? If it's ATA, turn off write cache with (atacontrol(8) or
> the sysctl.
> 
> The problem is that disks lie about whether they have actually written
> data. If the power goes off before the data is in cache, it's lost.
> 
> I am not sure if write-cache can be turned off on SCSI, but SCSI drives
> seem less likely to lie about when the data is actually flushed to the
> drive. 

At least you can set FUA if you want to force the data onto the platter.

-- 
Wilko Bulte				wilko at FreeBSD.org