From owner-freebsd-questions Mon Nov 26 20:57:56 2001 Delivered-To: freebsd-questions@freebsd.org Received: from mail5.nc.rr.com (fe5.southeast.rr.com [24.93.67.52]) by hub.freebsd.org (Postfix) with ESMTP id A773D37B41A for ; Mon, 26 Nov 2001 20:57:52 -0800 (PST) Received: from i8k.babbleon.org ([66.57.85.154]) by mail5.nc.rr.com with Microsoft SMTPSVC(5.5.1877.687.68); Mon, 26 Nov 2001 23:57:50 -0500 Content-Type: text/plain; charset="iso-8859-1" From: Brian T.Schellenberger To: Bob Willcox Subject: Re: Softupdates Date: Mon, 26 Nov 2001 23:57:36 -0500 X-Mailer: KMail [version 1.2] Cc: "Patrick O'Reilly" , Nils Holland , FreeBSD Question List References: <01112609195201.00903@i8k.babbleon.org> <20011126172050.A63285@luke.immure.com> In-Reply-To: <20011126172050.A63285@luke.immure.com> MIME-Version: 1.0 Message-Id: <01112623573601.00696@i8k.babbleon.org> Content-Transfer-Encoding: 8bit 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 Monday 26 November 2001 18:20, Bob Willcox wrote: > On Mon, Nov 26, 2001 at 09:19:52AM -0500, Brian T.Schellenberger wrote: > > [snip] > > > Also, you most definately should turn off write-caching if you turn on > > softupdates. In fact, you should do this anyway: softupdates are really > > rather safe, but write caching is quite dangerous, and doubly so with > > softupdates enabled. > > > > To do this, set > > > > hw.ata.wc=0 > > > > in your /boot/loader.conf (assuming IDE devices). If you use softupdates *and* enable write caching then you will screw up your disk with a simple sequence like rm -r foo/* shutdown -p now because the softupdates process will just finish writing its updates before the power is clobbered. At least that happens with my hardward, so softupdates is not compatible with write-cache-enabled. And from what I can tell (no rigorous testing), softupdates w/o write cache is just as fast as non-softupdates w/ write cache, but lots safer. I know that I've crashed 8 times in the last 36 hours and I'm darn glad I don't enable write caching! (Of course that's not the norm, but sometimes I manage that sort of thing.) > > In my experience, the current crop of ATA disks (I mostly have IBM) > write _much_ slower with write caching disabled (on the order of a > magnitude or more). Consequently, I find disabling it most undesirable. > Instead, I suggest that you invest in a UPS so that your chance of > suddenly dropping power to the disk is acceptably low...this is what I > have done. (I don't think your average system crash where power stays > up should be a problem since the disk would then have time to flush its > cache.) > > BTW, the performance on SCSI disks doesn't seem to be nearly as adversly > affected by disabling write caching (perhaps due to their higher-level > command interface, esp. command tag queuing). > > Any disk experts out there should correct me on this if I'm off base > (but this has been my experience). > > [snip] > > > Bob -- Brian T. Schellenberger . . . . . . . bts@wnt.sas.com (work) Brian, the man from Babble-On . . . . bts@babbleon.org (personal) http://www.babbleon.org -------> Free Dmitry Sklyarov! (let him go home) <----------- http://www.eff.org http://www.programming-freedom.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message