From: Theodore Tso Subject: Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: document conditions when reliable operation is possible) Date: Sun, 30 Aug 2009 11:20:23 -0400 Message-ID: <20090830152023.GB23828@mit.edu> 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> <4A9733C1.2070904@redhat.com> <20090828064449.GA27528@elf.ucw.cz> <20090828120854.GA8153@mit.edu> <20090830075135.GA1874@ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: NeilBrown , Ric Wheeler , Rob Landley , 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: Content-Disposition: inline In-Reply-To: <20090830075135.GA1874@ucw.cz> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Sun, Aug 30, 2009 at 09:51:35AM +0200, Pavel Machek wrote: > > If it only was this simple. We don't have 'check brakes' (aka > 'journalling ineffective') warning light. If we had that, I would not > have problem. But we do; comptently designed (and in the cast of software RAID, competently packaged) RAID subsystems send notifications to the system administrator when there is a hard drive failure. Some hardware RAID systems will send a page to the system administrator. A mid-range Areca card has a separate ethernet port so it can send e-mail to the administrator, even if the OS is hosed for some reason. And it's not a matter of journalling ineffective; the much bigger deal is, "your data is at risk"; perhaps because the file system metadata may become subject to corruption, but more critically, because the file data may become subject to corruption. Metadata becoming subject to corruption is important primarily because it leads to data becoming corruption; metadata is the tail; the user's data is the dog. So we *do* have the warning light; the problem is that just as some people may not realize that "check brakes" means, "YOU COULD DIE", some people may not realize that "hard drive failure; RAID array degraded" could mean, "YOU COULD LOSE DATA". Fortunately, for software RAID, this is easily solved; if you are so concerned, why don't you submit a patch to mdadm adjusting the e-mail sent to the system administrator when the array is in a degraded state, such that it states, "YOU COULD LOSE DATA". I would gently suggest to you this would be ***far*** more effective that a patch to kernel documentation. - Ted