From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261374AbVE2XFJ (ORCPT ); Sun, 29 May 2005 19:05:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261376AbVE2XFJ (ORCPT ); Sun, 29 May 2005 19:05:09 -0400 Received: from animx.eu.org ([216.98.75.249]:59308 "EHLO animx.eu.org") by vger.kernel.org with ESMTP id S261374AbVE2XE4 (ORCPT ); Sun, 29 May 2005 19:04:56 -0400 Date: Sun, 29 May 2005 19:01:38 -0400 From: Wakko Warner To: Mikulas Patocka Cc: linux-kernel@vger.kernel.org Subject: Re: RAID-5 design bug (or misfeature) Message-ID: <20050529230137.GA18854@animx.eu.org> Mail-Followup-To: Mikulas Patocka , linux-kernel@vger.kernel.org References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.6+20040907i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Mikulas Patocka wrote: > RAID-5 has rather serious design bug --- when two disks become temporarily > inaccessible (as it happened to me because of high temperature in server > room), linux writes information about these errors to the remaining disks > and when failed disks are on line again, RAID-5 won't ever be accessible. I ran into this myself, however, I had 10 disks (5 per channel) and one chennel went down. Ok, my array was dead at that point and I had to reboot. What luck, the arry wasn't usable anymore. My /usr was on that array, but my / was not. I did not want to go through the initrd/initramfs thing at the time to setup my / with raid5, plus the fact you truely cannot boot from it (thus partitioning and setting aside a slice wasn't viable to me) > RAID-HOWTO lists some actions that can be done in this case, but none of > them can be done if root filesystem is on RAID --- the machine just won't > boot. I had to reconstruct the array by hand with mdadm. evms wouldn't touch it. Fortunately, I had a copy of each disk's information and the raid5's information in files so it was quite easy to rebuild. I did have backups but that wasn't really what I wanted to do. (It did take over 2 hours before I could return to normal. evms can't handle a raid5 that was in reconstruction. I think newer versions have this fixed.) > I think Linux should stop accessing all disks in RAID-5 array if two disks > fail and not write "this array is dead" in superblocks on remaining disks, > efficiently destroying the whole array. That'd be nice =) -- Lab tests show that use of micro$oft causes cancer in lab animals