From owner-freebsd-fs Fri Oct 2 15:04:13 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id PAA12706 for freebsd-fs-outgoing; Fri, 2 Oct 1998 15:04:13 -0700 (PDT) (envelope-from owner-freebsd-fs@FreeBSD.ORG) Received: from smtp02.primenet.com (smtp02.primenet.com [206.165.6.132]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id PAA12595; Fri, 2 Oct 1998 15:04:01 -0700 (PDT) (envelope-from tlambert@usr08.primenet.com) Received: (from daemon@localhost) by smtp02.primenet.com (8.8.8/8.8.8) id PAA12256; Fri, 2 Oct 1998 15:03:42 -0700 (MST) Received: from usr08.primenet.com(206.165.6.208) via SMTP by smtp02.primenet.com, id smtpd012230; Fri Oct 2 15:03:41 1998 Received: (from tlambert@localhost) by usr08.primenet.com (8.8.5/8.8.5) id PAA21941; Fri, 2 Oct 1998 15:03:35 -0700 (MST) From: Terry Lambert Message-Id: <199810022203.PAA21941@usr08.primenet.com> Subject: Re: filesystem safety and SCSI disk write caching To: gibbs@plutotech.com (Justin T. Gibbs) Date: Fri, 2 Oct 1998 22:03:35 +0000 (GMT) Cc: julian@whistle.com, Don.Lewis@tsc.tdk.com, freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG In-Reply-To: <199810021953.NAA12817@pluto.plutotech.com> from "Justin T. Gibbs" at Oct 2, 98 01:46:43 pm X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > >write caching can screw soft updates if there is any > >major re-ordering of the data written. > > Only if you lose power or have a buggy device. Go read the SCSI spec on > write caching. > > >With tags it doesn't matter if they are re-ordered, as long > >as they are not acknowledged until they are on the platter. > > Tagged transactions may "complete" in a non-FIFO order. "Complete" either > means data transfered into the cache or data safely on the media depending > on whether the cache is enabled. Re-ordered writes are allowed, but, only > such that it maintains read/write coherency. This is with the restrictive > ordering semantics that drives usually ship with by default. You can turn > on "re-order at will" through a mode page. > > Waiting for Terry's long winded response to this thread, I told you so. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message