From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753299AbZH0VvJ (ORCPT ); Thu, 27 Aug 2009 17:51:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753266AbZH0VvF (ORCPT ); Thu, 27 Aug 2009 17:51:05 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:37594 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753205AbZH0VvF (ORCPT ); Thu, 27 Aug 2009 17:51:05 -0400 Date: Thu, 27 Aug 2009 23:50:56 +0200 From: Pavel Machek To: Chris Adams Cc: Theodore Tso , linux-kernel@vger.kernel.org Subject: Re: [patch] document flash/RAID dangers Message-ID: <20090827215056.GA1461@ucw.cz> References: <20090826134045.GA1516467@hiwaay.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090826134045.GA1516467@hiwaay.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! > The other thing about this thread is that the only RAID implementation > that is being discussed here is the MD RAID stack. There are a lot of > RAID implementations that have the same issues: > > - motherboard (aka "fake") RAID - In Linux this is typically mapped with > device mapper via dmraid; AFAIK there is not a tool to scrub (or even > monitor the status of and notify on failure) a Linux DM RAID setup. > > - hardware RAID cards without battery backup - these have the exact same > issues because they cannot guarantee all writes complete, nor can they > keep track of incomplete writes across power failures > > - hardware RAID cards _with_ battery backup but that don't periodically > test the battery and have a way to notify you of battery failure while > Linux is running > > The issues being raised here are not specific to extX, MD RAID, or Linux > at all; they are problems with non-"enterprise-class" RAID setups. > There's a reason enterprise-class RAID costs a lot more money than the > card you can pick up at Fry's. > > There's no reason to document the design issues of general RAID > implementations in the Linux kernel. Even when we carry one of those misdesigned implementations in-tree? (Note that fixed implementations do exist -- AIX? -- just add journal). 'I wont't tell you that this pony bites, because many ponies do bite'? WTF? I thought we had higher moral standard than this. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html