Date: 14 Jul 2005 18:09:07 -0400 From: Lowell Gilbert <freebsd-stable-local@be-well.ilk.org> To: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org Subject: Re: dangerous situation with shutdown process Message-ID: <447jftrqf0.fsf@be-well.ilk.org> 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 <jd@ugcs.caltech.edu> writes: > softupdates is perfectly safe with SCSI. > > its well known that ide and sata w/wo ncq fails to provide suitable > semantics for softupdates > > however, journaling fairs no better, and request barriers do nothing to > solve the problem. I had assumed that the sequence of operations in a journal would be idempotent. Is that a reasonable design criterion? [If it is, then it would make up for the fact that you can't build a reliable transaction gate. That is, you would just have to go back far enough that you *know* all of the needed journal is within the range you will replay. But even then, the journal would need to be on a separate medium, one that doesn't have the "lying to you about transaction completion" problem.] > On Thu, 14 Jul 2005, Matthias Buelow wrote: > > > Kevin Oberman wrote: > > > > >SCSI or ATA? If it's ATA, turn off write cache with (atacontrol(8) or > > >the sysctl. > > > > You do NOT want to do that. Not only will performance drop brutally > > (example: drop to 1/5th of normal write speed for sequential writes, > > probably worse for random writes) but it will also significantly > > reduce the lifetime of your disk. Modern disks are designed to be > > used with the write-back cache enabled, so don't turn it off. I have no idea what "designed to be used with the write-back cache enabled" could affect the operating life of the disk.
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