From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dan Merillat" Subject: Re: limits on raid Date: Sat, 16 Jun 2007 00:40:17 -0400 Message-ID: References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18035.23867.576212.859440@notabene.brown> Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Wakko Warner , david@lang.hm, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids > 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?