From owner-freebsd-current@FreeBSD.ORG Mon Jul 26 22:31:13 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 32E5D16A4CE; Mon, 26 Jul 2004 22:31:13 +0000 (GMT) Received: from mail.dt.e-technik.uni-dortmund.de (mail.dt.e-technik.Uni-Dortmund.DE [129.217.163.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7584F43D2D; Mon, 26 Jul 2004 22:31:12 +0000 (GMT) (envelope-from ma@dt.e-technik.uni-dortmund.de) Received: from m2a2.dyndns.org (p5487CB64.dip.t-dialin.net [84.135.203.100]) 42531365E4; Tue, 27 Jul 2004 00:31:11 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by merlin.emma.line.org (Postfix) with ESMTP id D6E3EB9CE7; Tue, 27 Jul 2004 00:31:08 +0200 (CEST) Received: from merlin.emma.line.org ([127.0.0.1]) by localhost (m2a2.dyndns.org [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 28276-04-3; Tue, 27 Jul 2004 00:31:07 +0200 (CEST) Received: by merlin.emma.line.org (Postfix, from userid 500) id DE1BAB9925; Tue, 27 Jul 2004 00:31:06 +0200 (CEST) To: Scott Long In-Reply-To: <20040726155712.R32601@pooker.samsco.org> (Scott Long's message of "Mon, 26 Jul 2004 16:06:33 -0600 (MDT)") References: <1090718450.2020.4.camel@illusion.com> <200407251112.46183.doconnor@gsoft.com.au> <20040726175219.GA96815@green.homeunix.org> <20040726155712.R32601@pooker.samsco.org> From: Matthias Andree Date: Tue, 27 Jul 2004 00:31:06 +0200 Message-ID: User-Agent: Gnus/5.110003 (No Gnus v0.3) Emacs/21.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: by amavisd-new at m2a2.dyndns.org cc: Matthias Andree cc: current@freebsd.org cc: bugghy Subject: Re: magic sysrq keys functionality X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 26 Jul 2004 22:31:13 -0000 Scott Long writes: > I don't believe that any order is guaranteed. FreeBSD used to have the > concept of a B_ORDERED bio flag that would help order the bioq, but it was > removed early in the 5-current cycle due to apparent non-use. It's tough > to rely on ATA Flush Cache since many devices exist that advertise it but > don't actually support it (i.e. they lock up if you try it). I have more devices that don't even advertise it than such that do... Out of four drives I've checked (Seagate, WDC, I*M DeathStar, Maxtor) only the latter, a Maxtor 4K060H3, advertises this. > SCSI certainly supports it, but again it was information that was > never getting to the device. Some SCSI drivers compensate by sending > periodic ordered tags to help decrease the chances for an out-of-order > commit, but it's still a small gamble. This works right now because > we assume that disks will commit blocks in order, and that assumption > generally hasn't been broken. The assumption is that the Queue Algorithm Modifier (offset 3, upper nibble) in the Control Mode Page (0xA) of the device is zero. If it's set to 1, the assumption is broken and so is consistency unless ordered tags are scheduled to enforce ordering. > If legacy ATA were to drop off the face of the earth and drive makers > were to commit to producing honest and non-buggy firmware, I'd love to > bring back B_ORDERED and make it actually work. FreeBSD 7 may be legacy-ATA free perhaps, or 6 if it takes a few years until then. -- Matthias Andree Encrypted mail welcome: my GnuPG key ID is 0x052E7D95 (PGP/MIME preferred)