From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263688AbTDTTpP (ORCPT ); Sun, 20 Apr 2003 15:45:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263690AbTDTTpP (ORCPT ); Sun, 20 Apr 2003 15:45:15 -0400 Received: from 81-2-122-30.bradfords.org.uk ([81.2.122.30]:7553 "EHLO 81-2-122-30.bradfords.org.uk") by vger.kernel.org with ESMTP id S263688AbTDTTpP (ORCPT ); Sun, 20 Apr 2003 15:45:15 -0400 From: John Bradford Message-Id: <200304202000.h3KK0GsX000976@81-2-122-30.bradfords.org.uk> Subject: Re: Are linux-fs's drive-fault-tolerant by concept? To: alan@lxorguk.ukuu.org.uk (Alan Cox) Date: Sun, 20 Apr 2003 21:00:16 +0100 (BST) Cc: skraw@ithnet.com (Stephan von Krawczynski), john@grabjohn.com (John Bradford), linux-kernel@vger.kernel.org (Linux Kernel Mailing List) In-Reply-To: <1050864521.11658.8.camel@dhcp22.swansea.linux.org.uk> from "Alan Cox" at Apr 20, 2003 07:48:42 PM X-Mailer: ELM [version 2.5 PL6] MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > > I know you favor a layer between low-level driver and fs > > probably. Sure it is clean design, and sure it sounds like > > overhead (Yet Another Layer). > > Wrong again - its actually irrelevant to the cost of mirroring data, the cost > is entirely in the PCI and memory bandwidth. The raid1 management overhead is > almost nil Actually what I was suggesting was even simpler - in the unlikely event that we were talking about an MFM or similar interface disk that _was_ basically like a big floppy, and did no error correction of it's own, we _could_ reserve, say, one sector per track, and create a fault tollerant device that substituted the spare sector in the event of a write fault. The overhead would probably be exactly zero, becuase nobody would actually compile the feature in and use it :-). John.