From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263807AbTDUKOP (ORCPT ); Mon, 21 Apr 2003 06:14:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263808AbTDUKOP (ORCPT ); Mon, 21 Apr 2003 06:14:15 -0400 Received: from mail.ithnet.com ([217.64.64.8]:39695 "HELO heather.ithnet.com") by vger.kernel.org with SMTP id S263807AbTDUKOM (ORCPT ); Mon, 21 Apr 2003 06:14:12 -0400 Date: Mon, 21 Apr 2003 12:25:44 +0200 From: Stephan von Krawczynski To: John Bradford Cc: vda@port.imtp.ilyichevsk.odessa.ua, adilger@clusterfs.com, john@grabjohn.com, linux-kernel@vger.kernel.org Subject: Re: Are linux-fs's drive-fault-tolerant by concept? Message-Id: <20030421122544.5ae6bd6f.skraw@ithnet.com> In-Reply-To: <200304210942.h3L9gZ1W000282@81-2-122-30.bradfords.org.uk> References: <200304210917.h3L9HIu07472@Port.imtp.ilyichevsk.odessa.ua> <200304210942.h3L9gZ1W000282@81-2-122-30.bradfords.org.uk> Organization: ith Kommunikationstechnik GmbH X-Mailer: Sylpheed version 0.8.11 (GTK+ 1.2.10; i686-pc-linux-gnu) 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 On Mon, 21 Apr 2003 10:42:35 +0100 (BST) John Bradford wrote: > > > > > > > I wonder whether it would be a good idea to give the linux-fs > > > > > > > (namely my preferred reiser and ext2 :-) some > > > > > > > fault-tolerance. > > > > > > I'm not against this in principle, but in practise it is almost > > > useless. Modern disk drives do bad sector remapping at write time, so > > > unless something is terribly wrong you will never see a write error > > > (which is exactly the time that the filesystem could do such > > > remapping). Normally, you will only see an error like this at read > > > time, at which point it is too late to fix. > > > > It is *not* useless. > > > > I have at least 4 disks with some bad sectors. Know what? > > They are still in use in a school lab and as 'big diskettes' > > (transferring movies etc). I refuse to dump them just because > > 'todays disks are cheap'. I don't want my fs to die just because > > these disks develop (ohhhh) a single new bad sector. > > Read my previous posts. > > A layer between device and filesystem can solve this. It doesn't > belong in the filesystem. Yes it _can_, but is it _intelligent_ to do it there? Ok, lets do it vice versa: What do you need to do it? - a free/allocated block list (for knowing where to put the mapped block) - a bad block list for monitoring purposes - spare blocks for really putting the data in You say: we re-invent/re-install the above information in a new layer. In this case you have the problem to find known-to-be-free blocks. In other words, you have to pre-alloc blocks (a fixed number) on the device, because else you interfer with fs. fs must not see your mapped-blocks-in-spe, or else will use them sooner or later. In other words you _waste_ them in case they are never needed. I say: we already have the needed information inside every fs, why not use it? No space wasted, no double information. If you say "it does not belong to fs" then please tell me: where in what bible do you read that? Your argument sounds like "god-given" to me. Do you see simple argueable technical issues? I do not say it is _easy_ to do, I say it is an intelligent option. Note the difference. Regards, Stephan