Date: Thu, 14 Jul 2005 22:31:44 +0200 From: Matthias Buelow <mkb@incubus.de> To: Jon Dama <jd@ugcs.caltech.edu> Cc: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org Subject: Re: dangerous situation with shutdown process Message-ID: <20050714203144.GC23666@drjekyll.mkbuelow.net> In-Reply-To: <Pine.LNX.4.53.0507141259320.536@spew.ugcs.caltech.edu> References: <42D6B117.5080302@plab.ku.dk> <20050714191449.A8A615D07@ptavv.es.net> <20050714195253.GA23666@drjekyll.mkbuelow.net> <Pine.LNX.4.53.0507141259320.536@spew.ugcs.caltech.edu>
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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.
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