From: Pavel Machek Subject: Re: [patch] document flash/RAID dangers Date: Wed, 26 Aug 2009 02:44:31 +0200 Message-ID: <20090826004430.GR4300@elf.ucw.cz> References: <20090825094244.GC15563@elf.ucw.cz> <20090825161110.GP17684@mit.edu> <20090825222112.GB4300@elf.ucw.cz> <20090825224004.GD4300@elf.ucw.cz> <20090825233701.GH4300@elf.ucw.cz> <20090826001206.GL4300@elf.ucw.cz> <4A94812C.5010803@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: david@lang.hm, Theodore Tso , Florian Weimer , Goswin von Brederlow , Rob Landley , 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: Ric Wheeler Return-path: Content-Disposition: inline In-Reply-To: <4A94812C.5010803@redhat.com> Sender: linux-doc-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org >>>> THESE devices have the property of potentially corrupting blocks being >>>> written at the time of the power failure, >>> >>> this is true of all devices >> >> Actually I don't think so. I believe SATA disks do not corrupt even >> the sector they are writing to -- they just have big enough >> capacitors. And yes I believe ext3 depends on that. > > Pavel, no S-ATA drive has capacitors to hold up during a power failure > (or even enough power to destage their write cache). I know this from > direct, personal knowledge having built RAID boxes at EMC for years. In > fact, almost all RAID boxes require that the write cache be hardwired to > off when used in their arrays. I never claimed they have enough power to flush entire cache -- read the paragraph again. I do believe the disks have enough capacitors to finish writing single sector, and I do believe ext3 depends on that. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html