From owner-freebsd-questions Wed Aug 29 22:19:39 2001 Delivered-To: freebsd-questions@freebsd.org Received: from guru.mired.org (okc-94-248-46.mmcable.com [24.94.248.46]) by hub.freebsd.org (Postfix) with SMTP id B258537B401 for ; Wed, 29 Aug 2001 22:19:34 -0700 (PDT) (envelope-from mwm@mired.org) Received: (qmail 7066 invoked by uid 100); 30 Aug 2001 05:19:33 -0000 From: Mike Meyer MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <15245.52453.614096.245669@guru.mired.org> Date: Thu, 30 Aug 2001 00:19:33 -0500 To: Trevin Chow Cc: Mike Meyer , Subject: Re: Performance tuning and adding RAM In-Reply-To: <20010829215734.F79672-100000@benny.geektank.org> References: <15245.36122.131328.798913@guru.mired.org> <20010829215734.F79672-100000@benny.geektank.org> X-Mailer: VM 6.90 under 21.1 (patch 14) "Cuyahoga Valley" XEmacs Lucid X-face: "5Mnwy%?j>IIV\)A=):rjWL~NB2aH[}Yq8Z=u~vJ`"(,&SiLvbbz2W`;h9L,Yg`+vb1>RG% *h+%X^n0EZd>TM8_IB;a8F?(Fb"lw'IgCoyM.[Lg#r\ Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Trevin Chow 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. For IDE drives, you disable this by setting the sysctl hw.ata.wc to 0, but it has to be done from the boot loader at boot time. If you are running 4.3-RELEASE, it's set off by default. If you're running something prior to 4.3-RELEASE, you may not be able to set it at all. The drive manufacturer may provide a DOS utility that will let you turn it off as well. 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. 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