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To: Matthias Buelow <mkb@incubus.de>
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From: Lowell Gilbert <freebsd-stable-local@be-well.ilk.org>
Date: 15 Jul 2005 16:15:27 -0400
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Cc: John-Mark Gurney <gurney_j@resnet.uoregon.edu>, freebsd-stable@freebsd.org
Subject: Re: dangerous situation with shutdown process
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Matthias Buelow <mkb@incubus.de> writes:

> The combination barriers+journal really seems to be very resilient
> to filesystem corruption. When it's implemented without errors, and
> the hardware doesn't do things like change bits randomly, I can't
> think of a way this scheme can be corrupted at all.

We keep trying to point out that barriers *can't* be enforced on the
hardware with many (most, and apparently an increasing percentage of)
ATA drives.  There is no semantic on these drives that allows you to
guarantee the journal block will be written before the corresponding
data block.  If you are sure that your drives do this properly, then
you are safe, but in that case there's no reliability problem with
softupdates, either.