From: Ric Wheeler Subject: Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: document conditions when reliable operation is possible) Date: Thu, 27 Aug 2009 21:32:49 -0400 Message-ID: <4A9733C1.2070904@redhat.com> References: <20090824212518.GF29763@elf.ucw.cz> <20090825232601.GF4300@elf.ucw.cz> <4A947682.2010204@redhat.com> <200908262253.17886.rob@landley.net> <4A967175.5070700@redhat.com> <20090827221319.GA1601@ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Rob Landley , Theodore Tso , Florian Weimer , Goswin von Brederlow , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net To: Pavel Machek Return-path: In-Reply-To: <20090827221319.GA1601@ucw.cz> Sender: linux-doc-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 08/27/2009 06:13 PM, Pavel Machek wrote: > >>>> Repeat experiment until you get up to something like google scale or the >>>> other papers on failures in national labs in the US and then we can have an >>>> informed discussion. >>>> >>> On google scale anvil lightning can fry your machine out of a clear sky. >>> >>> However, there are still a few non-enterprise users out there, and knowing >>> that specific usage patterns don't behave like they expect might be useful to >>> them. >> >> You are missing the broader point of both papers. They (and people like >> me when back at EMC) look at large numbers of machines and try to fix >> what actually breaks when run in the real world and causes data loss. >> The motherboards, S-ATA controllers, disk types are the same class of >> parts that I have in my desktop box today. > ... >> These errors happen extremely commonly and are what RAID deals with well. >> >> What does not happen commonly is that during the RAID rebuild (kicked >> off only after a drive is kicked out), you push the power button or have >> a second failure (power outage). >> >> We will have more users loose data if they decide to use ext2 instead of >> ext3 and use only single disk storage. > > So your argument basically is > > 'our abs brakes are broken, but lets not tell anyone; our car is still > safer than a horse'. > > and > > 'while we know our abs brakes are broken, they are not major factor in > accidents, so lets not tell anyone'. > > Sorry, but I'd expect slightly higher moral standards. If we can > document it in a way that's non-scary, and does not push people to > single disks (horses), please go ahead; but you have to mention that > md raid breaks journalling assumptions (our abs brakes really are > broken). > Pavel > You continue to ignore the technical facts that everyone (both MD and ext3) people put in front of you. If you have a specific bug in MD code, please propose a patch. Ric