Date: Thu, 30 Aug 2001 20:22:06 -0500 From: "Jim C. Nasby" <jim@nasby.net> To: Mike Meyer <mwm@mired.org> Cc: Trevin Chow <tmchow@sfu.ca>, questions@freebsd.org Subject: SCSI write caching (was: Re: Performance tuning and adding RAM) Message-ID: <20010830202206.R63459@enteract.com> In-Reply-To: <15245.52453.614096.245669@guru.mired.org>; from mwm@mired.org on Thu, Aug 30, 2001 at 12:19:33AM -0500 References: <15245.36122.131328.798913@guru.mired.org> <20010829215734.F79672-100000@benny.geektank.org> <15245.52453.614096.245669@guru.mired.org>
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On Thu, Aug 30, 2001 at 12:19:33AM -0500, Mike Meyer wrote: > Trevin Chow <tmchow@sfu.ca> types: > > On Wed, 29 Aug 2001, Mike Meyer wrote: > > > The reliability of soft updates is dependent on knowing that data > > > written to disk is actually on the disk. If you turn on softupdates, > > > turn off write cache on your disk drives. > > I'm confused by your last statement. Why do I turn off write cache on my > > HDs? Are you talking about another sysctl variable or in teh actual bios? > > I'm talking about a (mis)feature that some hard disks have. To quote > the tuning(7) man page: > > With IDE write caching turned on, IDE hard drives will not only > write data to disk out of order, they will sometimes delay some of > the blocks indefinitely when under heavy disk loads. > <snip> > > If you are using SCSI disks, you can use the camcontrol modepage > command to check and disable it. It's the WCE value on page 8; use > "camcontrol modepage daX -m 8 -e" to start an editor, change the 1 to > a 0, and then exit. Is this also necessary with SCSI drives? I was under the impression that they weren't susceptible to this problem... > > <mike > -- > Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ > Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message -- Jim C. Nasby (aka Decibel!) jim@nasby.net Member: Triangle Fraternity, Sports Car Club of America Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?" To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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