Date: Thu, 14 Jul 2005 15:12:36 -0500 From: David Sze <dsze@distrust.net> To: Matthias Buelow <mkb@incubus.de> Cc: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org Subject: Re: dangerous situation with shutdown process Message-ID: <20050714201236.GA15856@mail.distrust.net> 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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On Thu, Jul 14, 2005 at 09:52:53PM +0200, Matthias Buelow wrote: > Kevin Oberman wrote: > > >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). > > Until a journalled fs that uses write request barriers is available > for FreeBSD, you better had a reliable UPS. How do OS-level request barriers help if the disk reorders pending writes in its cache?
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