From owner-freebsd-stable@FreeBSD.ORG Fri Jan 21 16:49:31 2005 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 0F8C316A4CE for ; Fri, 21 Jan 2005 16:49:31 +0000 (GMT) Received: from av7-1-sn4.m-sp.skanova.net (av7-1-sn4.m-sp.skanova.net [81.228.10.110]) by mx1.FreeBSD.org (Postfix) with ESMTP id 865F943D31 for ; Fri, 21 Jan 2005 16:49:30 +0000 (GMT) (envelope-from ertr1013@student.uu.se) Received: by av7-1-sn4.m-sp.skanova.net (Postfix, from userid 502) id BB5AD37E84; Fri, 21 Jan 2005 17:49:29 +0100 (CET) Received: from smtp4-2-sn4.m-sp.skanova.net (smtp4-2-sn4.m-sp.skanova.net [81.228.10.180]) by av7-1-sn4.m-sp.skanova.net (Postfix) with ESMTP id ACD0637E42 for ; Fri, 21 Jan 2005 17:49:29 +0100 (CET) Received: from falcon.midgard.homeip.net (h201n1fls24o1048.bredband.comhem.se [212.181.162.201]) by smtp4-2-sn4.m-sp.skanova.net (Postfix) with SMTP id 7FC8E37E42 for ; Fri, 21 Jan 2005 17:49:29 +0100 (CET) Received: (qmail 50949 invoked by uid 1001); 21 Jan 2005 16:49:29 -0000 Date: Fri, 21 Jan 2005 17:49:29 +0100 From: Erik Trulsson To: Kevin Oberman Message-ID: <20050121164928.GA50279@falcon.midgard.homeip.net> Mail-Followup-To: Kevin Oberman , Mark Kirkwood , freebsd-stable@freebsd.org, "Jim C. Nasby" References: <41F0B4E8.9090507@paradise.net.nz> <20050121163106.B01855D08@ptavv.es.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050121163106.B01855D08@ptavv.es.net> User-Agent: Mutt/1.5.6i cc: freebsd-stable@freebsd.org cc: Mark Kirkwood cc: "Jim C. Nasby" Subject: Re: Disabling write-behind on IDE drives, and SMART X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Jan 2005 16:49:31 -0000 On Fri, Jan 21, 2005 at 08:31:06AM -0800, Kevin Oberman wrote: > > Date: Fri, 21 Jan 2005 20:53:12 +1300 > > From: Mark Kirkwood > > Sender: owner-freebsd-stable@freebsd.org > > > > Jim C. Nasby wrote: > > > Question one: how do I disable write caching on IDE drives? I know the > > > setting is hw.ata.wc=0, but where do I put that? In loader.conf? This is > > > FreeBSD 4.10, btw. > > > > > In /boot/loader.conf will do it. > > > > > Also, has any thought been given to making the default 0, like it is for > > > SCSI devices? I'm honestly surprised and disappointed that the default > > > is speed over data integrity. > > I think it was trialled in 4.3 then changed for 4.4 (according to the > > handbook, the performance hit was considered to be too high) > > Having been involved in the 4.x flip-flop, the performance cost on some > systems can be HUGE! Backing up my laptop (40 GB) went from 40 minutes > to five hours when the write cache was turned off. > > On the other hand, it is a real risk, especially when combined with > softupdates. I don't see how softupdates can increase the risk. As I understand it the risks with IDE-write chaching is just as large with softupdates as without. It is just that all the safety and consistency guarantees that softupdates normally make go out of the window when write-caching is turned on. > For servers that lack solid backup power (not a 10 minute > UPS), I would probably turn it off. But for most systems it is probably > worth the risks. A 10 minute UPS should be plenty for that purpose. All that is needed to protect against the risks of write-caching is for the server to be able to make an orderly shutdown, which should not take more than a couple of minutes. (If you need constant uptime, you need better power backup, but that is a different issue.) -- Erik Trulsson ertr1013@student.uu.se