dangerous situation with shutdown process

[Kevin Oberman]

> 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. 
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634