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Date: Thu, 14 Jul 2005 22:31:44 +0200
From: Matthias Buelow <mkb@incubus.de>
To: Jon Dama <jd@ugcs.caltech.edu>
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Cc: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org
Subject: Re: dangerous situation with shutdown process
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Jon Dama wrote:

>Request Barriers under linux exist to prevent the low level kernel block
>device layer from reordering write operations from the upper file system
>layers.  Request Barriers consist of nothing more than tagging internal
>queues within the Linux kernel itself.  They do nothing to resolve the
>underlying failures of the hardware to provide proper semantics to the
>block device layer.
>but, Request Barriers are ultimately useless.  They can't resolve the
>underlying problems with ide/sata and there are already exposed semantics
>for scsi.

If you flush the cache at barriers, on-disk integrity of the journal
vs. metadata updates is guaranteed.

mkb.