Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754454AbXFPEk3 (ORCPT ); Sat, 16 Jun 2007 00:40:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750711AbXFPEkU (ORCPT ); Sat, 16 Jun 2007 00:40:20 -0400 Received: from ug-out-1314.google.com ([66.249.92.168]:29396 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751494AbXFPEkT (ORCPT ); Sat, 16 Jun 2007 00:40:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=RWSG/aSGiogtMrtWs5v5HpkbEa86YQ6I3Fy7ajLoHR+BAFvHXPwWhKYYrLxk+T8MbZkBaR54KFeg8+QS5t8CH0QRPtsa/X2luql+WNv0rySQFsF6KvuSgowtiHAPZ36NgPXAEdt+yzAEM+OaKq1ujHYLH6A9qvBSEn+/3SOq0og= Message-ID: Date: Sat, 16 Jun 2007 00:40:17 -0400 From: "Dan Merillat" To: "Neil Brown" Subject: Re: limits on raid Cc: "Wakko Warner" , david@lang.hm, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org In-Reply-To: <18035.23867.576212.859440@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1019 Lines: 22 > For raid5 on an array with more than 3 drive, if you attempt to write > a single block, it will: > > - read the current value of the block, and the parity block. > - "subtract" the old value of the block from the parity, and "add" > the new value. > - write out the new data and the new parity. > > If the parity was wrong before, it will still be wrong. If you then > lose a drive, you lose your data. Wow, that really needs to be put somewhere in 120 point red blinking text. A lot of us are used to uninitialized disks calculating the parity-on-first-write, but if linux MD is forgoeing that 'dangerous-no-resync' sounds really REALLY bad. How about at least a 'Warning: unlike other systems this WILL cause corruption if you forego reconstruction' on mkraid? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/