From owner-freebsd-scsi Fri Oct 2 12:53:37 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id MAA25026 for freebsd-scsi-outgoing; Fri, 2 Oct 1998 12:53:37 -0700 (PDT) (envelope-from owner-freebsd-scsi@FreeBSD.ORG) Received: from pluto.plutotech.com (mail.plutotech.com [206.168.67.137]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id MAA25020; Fri, 2 Oct 1998 12:53:34 -0700 (PDT) (envelope-from gibbs@plutotech.com) Received: from narnia.plutotech.com (narnia.plutotech.com [206.168.67.130]) by pluto.plutotech.com (8.8.7/8.8.5) with ESMTP id NAA12817; Fri, 2 Oct 1998 13:53:13 -0600 (MDT) Message-Id: <199810021953.NAA12817@pluto.plutotech.com> X-Mailer: exmh version 2.0.2 2/24/98 To: Julian Elischer cc: Don Lewis , freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG Subject: Re: filesystem safety and SCSI disk write caching In-reply-to: Your message of "Fri, 02 Oct 1998 11:59:26 PDT." Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 02 Oct 1998 13:46:43 -0600 From: "Justin T. Gibbs" Sender: owner-freebsd-scsi@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, Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message