Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758852AbYAQXVi (ORCPT ); Thu, 17 Jan 2008 18:21:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754621AbYAQXVa (ORCPT ); Thu, 17 Jan 2008 18:21:30 -0500 Received: from mexforward.lss.emc.com ([128.222.32.20]:14680 "EHLO mexforward.lss.emc.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753472AbYAQXV3 (ORCPT ); Thu, 17 Jan 2008 18:21:29 -0500 Message-ID: <478FE22D.9030907@emc.com> Date: Thu, 17 Jan 2008 18:18:05 -0500 From: Ric Wheeler User-Agent: Thunderbird 2.0.0.0 (X11/20070326) MIME-Version: 1.0 To: Theodore Tso , Daniel Phillips , Bryan Henderson , Al Boldi , Alan Cox , David Chinner , linux-kernel@vger.kernel.org, Pavel Machek , Rik van Riel , Valerie Henson Subject: Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck) References: <4d47a5d10801151724m418e18efp9a0dd936e9a3584c@mail.gmail.com> <4d47a5d10801161802x2c24ef59pf8422c8d14d487aa@mail.gmail.com> <20080117224530.GH5547@mit.edu> In-Reply-To: <20080117224530.GH5547@mit.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-PMX-Version: 4.7.1.128075, Antispam-Engine: 2.5.1.298604, Antispam-Data: 2007.8.30.53115 X-PerlMx-Spam: Gauge=, SPAM=1%, Reason='EMC_FROM_0+ -3, __CT 0, __CTE 0, __CT_TEXT_PLAIN 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __SANE_MSGID 0, __USER_AGENT 0' X-Tablus-Inspected: yes X-Tablus-Classifications: public X-Tablus-Action: allow Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1370 Lines: 33 Theodore Tso wrote: > On Wed, Jan 16, 2008 at 09:02:50PM -0500, Daniel Phillips wrote: >> Have you observed that in the wild? A former engineer of a disk drive >> company suggests to me that the capacitors on the board provide enough >> power to complete the last sector, even to park the head. >> Even if true (which I doubt), this is not implemented. A modern drive can have 16-32 MB of write cache. Worst case, those sectors are not sequential which implies lots of head movement. > > The problem isn't with the disk drive; it's from the DRAM, which tend > to be much more voltage sensitive than the hard drives --- so it's > quite likely that you could end up DMA'ing garbage from the memory. > In fact the fact that the disk drives lasts longer due to capacitors > on the board, rotational inertia of the platters, etc., is part of the > problem. I can tell you directly that when you drop power to a drive, you will lose write cache data if the write cache is enabled. With barriers enabled, our testing shows that file systems survive power failures which routinely caused corruption without them ;-) ric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/