From owner-freebsd-questions Wed Jan 30 18:28:59 2002 Delivered-To: freebsd-questions@freebsd.org Received: from mail8.nc.rr.com (fe8.southeast.rr.com [24.93.67.55]) by hub.freebsd.org (Postfix) with ESMTP id 92E3237B404 for ; Wed, 30 Jan 2002 18:28:52 -0800 (PST) Received: from i8k.babbleon.org ([66.57.85.154]) by mail8.nc.rr.com with Microsoft SMTPSVC(5.5.1877.687.68); Wed, 30 Jan 2002 20:17:07 -0500 Received: by i8k.babbleon.org (Postfix, from userid 111) id 10D3A4078; Wed, 30 Jan 2002 20:15:43 -0500 (EST) Content-Type: text/plain; charset="iso-8859-1" From: Brian T.Schellenberger To: "Scott Gerhardt" Subject: Re: Softupdates Date: Wed, 30 Jan 2002 20:15:42 -0500 X-Mailer: KMail [version 1.3] References: In-Reply-To: Cc: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-Id: <20020131011543.10D3A4078@i8k.babbleon.org> 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 On Wednesday 30 January 2002 03:43 pm, you wrote: > > Now it IS a bad idea (even though many people do it without > > happening to get > > burned) to run with write caching *and* softupdates both on. > > In general, > > it's a bad isea to run with write caching, period, but > > combining it with > > softupdates makes things a lot worse, but softupdates without > > write caching > > is safer than the other way 'round. Of course, turning both > > off is safest > > and slowest, so pick your poison. I use softupdates on ALL > > file systems and > > turn off write caching myself. > > > > (To turn off write-caching, put this in /boot/loader.conf: > > > > # write cache considered dangerous > > hw.ata.wc=0 > > ) > > > > The reason for the general advice to turn it off on / is > > because it does > > introduce a delay and / is traditionally rather small. The > > delay effectively > > gives you less space in a file system since freed space may > > not be freed yet, > > but if you make / larger than usual and turn on softupdates > > you'll get the > > speed benefit of softupdates and yet won't risk running out > > of disk space. > > > > (It seems an especial shame to turn off softupdates on > > whatever file system > > contains /tmp since the benefits are larger on a file system > > with lots of > > writes.) > > The write caching issue is more of an IDE-ATA issue. > As far as I know write caching is not such an issue with the newer SCSI > drives that have Tagged Queueing Enabled (see dmesg from one of my systems > below). > > > Excerpt from dmesg: > > da0 at ahc0 bus 0 target 0 lun 0 > da0: Fixed Direct Access SCSI-3 device > da0: 160.000MB/s transfers (80.000MHz, offset 63, 16bit), Tagged Queueing > Enabled > > I could be wrong, so correct me if I am. No, you are exactly correct. I think that the ideal would probably to be have write caching disabled for ata (IDE) and enabled for SCSI. But I do wish that in marginal cases the defaults were more conservative myself. > > Regards, > > - Scott > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message -- Brian T. Schellenberger . . . . . . . bts@wnt.sas.com (work) Brian, the man from Babble-On . . . . bts@babbleon.org (personal) ME --> http://www.babbleon.org http://www.eff.org <-- GOOD GUYS --> http://www.programming-freedom.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message