From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263637AbTDTRKN (ORCPT ); Sun, 20 Apr 2003 13:10:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263636AbTDTRKM (ORCPT ); Sun, 20 Apr 2003 13:10:12 -0400 Received: from 81-2-122-30.bradfords.org.uk ([81.2.122.30]:36480 "EHLO 81-2-122-30.bradfords.org.uk") by vger.kernel.org with ESMTP id S263637AbTDTRKL (ORCPT ); Sun, 20 Apr 2003 13:10:11 -0400 From: John Bradford Message-Id: <200304201725.h3KHP5lU000751@81-2-122-30.bradfords.org.uk> Subject: Re: Are linux-fs's drive-fault-tolerant by concept? To: 76306.1226@compuserve.com (Chuck Ebbert) Date: Sun, 20 Apr 2003 18:25:05 +0100 (BST) Cc: arjanv@redhat.com (arjanv@redhat.com), linux-kernel@vger.kernel.org (linux-kernel) In-Reply-To: <200304201306_MC3-1-3537-115@compuserve.com> from "Chuck Ebbert" at Apr 20, 2003 01:03:02 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 > >> You will if it writes and fails to read back. The disk can't invent a > >> sector that is gone. > > > > but linux can if you use an raid1 mirror... maybe we should teach the md > > layer to write back the data from the other disk on a "bad sector" > > error. > > > I have some ugly code that forces all reads from a mirror set to > a specific copy, set via a global sysctl. This lets you do things > like make a backup from disk 0, then verify against disk 1 and take > action if something is wrong. That's interesting. Have you thought of making it read from _both_ disks and check that the data matches, before passing it back? RAID1 mirrors guard against drive failiure, but if a drive returns bad data, but doesn't report an error, that will usually go unnoticed. By reading from both disks, and checking that the data was the same, we could guard against broken firmware. Of course, this would reduce performane quite a bit, but it might have some uses. John.