Date: Fri, 15 Jul 2005 11:54:13 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: Matthias Buelow <mkb@incubus.de> Cc: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org Subject: Re: dangerous situation with shutdown process Message-ID: <20050715185413.GI37261@funkthat.com> In-Reply-To: <20050714195253.GA23666@drjekyll.mkbuelow.net> References: <42D6B117.5080302@plab.ku.dk> <20050714191449.A8A615D07@ptavv.es.net> <20050714195253.GA23666@drjekyll.mkbuelow.net>
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Matthias Buelow wrote this message on Thu, Jul 14, 2005 at 21:52 +0200:
> >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.
>
> No, the problem is that FreeBSD doesn't implement request barriers
> and that softupdates is flawed by design and seemingly could not
> make use of them, even if they were available (because, as I
> understand it, it relies on a total ordering of all writes, unlike
> the partial ordering necessary for a journalled fs).
even request barries will not save the fs in a power loss if the track
that is getting flushed durning a power loss... Some other FreeBSD
folk has a reproducable case of where blocks that were not written to
on ATA hardware got trashed after a power loss...
With non-written to sectors getting trashed with the cache enabled,
barriers don't mean squat...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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