Date: Sat, 16 Jul 2005 00:03:49 +0200 From: Matthias Buelow <mkb@incubus.de> To: Lowell Gilbert <freebsd-stable-local@be-well.ilk.org> Cc: John-Mark Gurney <gurney_j@resnet.uoregon.edu>, freebsd-stable@freebsd.org Subject: Re: dangerous situation with shutdown process Message-ID: <200507152203.j6FM3nsL015084@drjekyll.mkbuelow.net> In-Reply-To: Message from Lowell Gilbert <freebsd-stable-local@be-well.ilk.org> of "15 Jul 2005 16:15:27 EDT." <44br539674.fsf@be-well.ilk.org>
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Lowell Gilbert <freebsd-stable-local@be-well.ilk.org> writes: >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. See my other mail(s) about other systems using cache disabling/enabling to make up for a drive that ignores (or does not implement) a flush command. Then the advice of "disable the wb-cache on disks to ensure data safety" doesn't make sense: Either * the drive supports disabling the write-back-cache, then this method can be used to flush data to the platters, or else * the drive does not support disabling the write-back-cache, or lies about it, then the advice to disable the write-back-cache for softupdates is meaningless. I know my drive allows disabling of the write cache, as, apparently, the majority of IDE/SATA drives do. mkb.
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