From owner-freebsd-hackers Mon Oct 28 21:44:59 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1A7CE37B401 for ; Mon, 28 Oct 2002 21:44:58 -0800 (PST) Received: from canning.wemm.org (canning.wemm.org [192.203.228.65]) by mx1.FreeBSD.org (Postfix) with ESMTP id CC33C43E4A for ; Mon, 28 Oct 2002 21:44:57 -0800 (PST) (envelope-from peter@wemm.org) Received: from wemm.org (localhost [127.0.0.1]) by canning.wemm.org (Postfix) with ESMTP id A905A2A88D; Mon, 28 Oct 2002 21:44:57 -0800 (PST) (envelope-from peter@wemm.org) X-Mailer: exmh version 2.5 07/13/2001 with nmh-1.0.4 To: "."@babolo.ru Cc: "Daniel O'Connor" , Chuck Robey , Kenneth Culver , "Wilkinson, Alex" , hackers@FreeBSD.ORG Subject: Re: [hardware] Tagged Command Queuing or Larger Cache ? In-Reply-To: <200210290542.g9T5g6PV036712@aaz.links.ru> Date: Mon, 28 Oct 2002 21:44:57 -0800 From: Peter Wemm Message-Id: <20021029054457.A905A2A88D@canning.wemm.org> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG "."@babolo.ru wrote: > > "Daniel O'Connor" wrote: > > As you can imagine, this violates the basic assumptions of FFS and softdep. > > They assume that only sectors that are written to are at risk, and do all > > their ordering based on that assumption. But the assumption is completely > > bogus. Even with no-caching it doesn't work because if the drive loses > > power after only having written half of the track, then you risk losing the > > rest - the track is written from "wherever", and not any index marks. ie: > > the track is just as likely to overwrite the second half of the sectors > > first, and when you lose power, you have two copies of the first half of > > the sectors. Basically you have to assume that the entire track and > > all of the nearby sectors could get lost or trashed. > I usually lose 4..8 sectors cluster on fast power down > on IBM IDE drives. > Repairable. Maybe so, but FFS is written with the assumption that only the sector being written is at risk. Even losing 4-8 sectors blows that out the window if it happens to be metadata. Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message