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Date:      16 Jul 2005 13:04:17 -0400
From:      Lowell Gilbert <freebsd-stable-local@be-well.ilk.org>
To:        Paul Mather <paul@gromit.dlib.vt.edu>
Cc:        freebsd-stable@freebsd.org, Matthias Buelow <mkb@incubus.de>
Subject:   Re: dangerous situation with shutdown process
Message-ID:  <44k6jqof72.fsf@be-well.ilk.org>
In-Reply-To: <1121530912.17757.32.camel@zappa.Chelsea-Ct.Org>
References:  <20050715224650.GA48516@outcold.yadt.co.uk> <200507152342.j6FNg5Tx015427@drjekyll.mkbuelow.net> <20050716133710.GA71580@outcold.yadt.co.uk> <20050716141630.GB752@drjekyll.mkbuelow.net> <1121530912.17757.32.camel@zappa.Chelsea-Ct.Org>

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Paul Mather <paul@gromit.dlib.vt.edu> writes:

> Despite that, I have never EVER had a problem with data consistency on
> my file systems.  (The only problem I have had is when I added an ATA
> controller card one time and forgot to disable its RAID BIOS, which
> promptly spammed over my geom_mirror metadata.:)  If softupdates were as
> unsafe as you often hint, I'm surprised that I haven't lost a file
> system by now.  (I would also expect to hear from the field a lot more
> clamour about how unsafe it is, and that, in fact, the sky was indeed
> falling.)  I guess I must be amazingly lucky and should start playing
> the lottery right now. :-)

Well, break it down a little bit.  If an ATA drive properly implements
the cache flush command, then none of the ongoing discussion is
relevant.  Herr Buelow is worried about drives that do *not* do so,
but which, when told to disable their cache, will reliably empty the
cache before continuing with further operations.  Such drives are the
only ones to which any of the discussion applies.

If such drives are reasonably common, then using such a hack would
make sense.  However, I would want some fairly solid evidence on the
matter before I was willing to start coding it, and so far the most
convincing evidence I have seen is that Microsoft engineers claim to
have done it.

Be well.



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