From owner-freebsd-stable Thu Jun 20 14:57:40 2002 Delivered-To: freebsd-stable@freebsd.org Received: from quack.kfu.com (adsl-67-113-12-90.dsl.snfc21.pacbell.net [67.113.12.90]) by hub.freebsd.org (Postfix) with ESMTP id DCC2637B410 for ; Thu, 20 Jun 2002 14:57:33 -0700 (PDT) Received: from kfu.com (gate.cenzic.com [66.237.77.34]) (authenticated) by quack.kfu.com (8.11.6/8.11.6) with ESMTP id g5KLvQt45913 (using TLSv1/SSLv3 with cipher RC4-MD5 (128 bits) verified OK); Thu, 20 Jun 2002 14:57:29 -0700 (PDT) (envelope-from nsayer@kfu.com) Message-ID: <3D124F7C.6090302@kfu.com> Date: Thu, 20 Jun 2002 14:56:12 -0700 From: Nick Sayer User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1a) Gecko/20020611 X-Accept-Language: en-us, en MIME-Version: 1.0 To: pjklist@ekahuna.com Cc: stable@FreeBSD.ORG, Matthias Andree Subject: Re: ATA Atapi 4.6 Release References: <20020620211121029.AAA600@empty1.ekahuna.com@pc02.ekahuna.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Philip J. Koenig wrote: > >Excuse my ignorance but I was under the impression that (at least >for SCSI) the sole function of tagged command queuing was to re-order >a string of drive commands in order to perform them more efficiently >- ie take into account sector position and latency to re-order things >like seeks. (ie "elevator sorting" or "elevator seeking") > >Why does this magically make write-back drive-caching "safe"? > Because the OS is notified when the write is actually completed. That makes it safe, because softupdates can insure that writes occur in a particular order (that is, write #2 is not scheduled until it is known that write #1 completes). To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message