From owner-freebsd-questions@FreeBSD.ORG Tue Jul 1 14:34:47 2008 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E8ACF106566C for ; Tue, 1 Jul 2008 14:34:47 +0000 (UTC) (envelope-from rvm@CBORD.com) Received: from smssmtp.cbord.com (mx1.cbord.com [24.39.174.11]) by mx1.freebsd.org (Postfix) with ESMTP id A714D8FC1E for ; Tue, 1 Jul 2008 14:34:47 +0000 (UTC) (envelope-from rvm@CBORD.com) X-AuditID: ac1f0165-00000d18000003dc-fe-486a409d00e0 Received: from Email.cbord.com ([10.1.1.100]) by smssmtp.cbord.com with Microsoft SMTPSVC(6.0.3790.1830); Tue, 1 Jul 2008 10:35:08 -0400 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Date: Tue, 1 Jul 2008 10:32:03 -0400 Message-ID: In-Reply-To: <80f4f2b20807010652w3a5215fas1f62ff682606e444@mail.gmail.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: filesystem information Thread-Index: AcjbgaiwvEjCLul2SSGs1eqehCpnuwAApWog References: <80f4f2b20806300401x71483882x8e9a6cf919f1ff9@mail.gmail.com><20080630073059.be11304d.wmoran@potentialtech.com><80f4f2b20806300930p67ca1fd5xf9ad59d16889df36@mail.gmail.com><20080630170400.GB65282@slackbox.xs4all.nl><80f4f2b20806301212n1bf6137bq75f40464212c2304@mail.gmail.com><20080701091048.GA31499@ei.bzerk.org> <80f4f2b20807010652w3a5215fas1f62ff682606e444@mail.gmail.com> From: "Bob McConnell" To: "Jim" , "Ruben de Groot" , "Roland Smith" , X-Brightmail-Tracker: AAAAAA== Cc: Subject: RE: filesystem information X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 01 Jul 2008 14:34:48 -0000 On Behalf Of Jim >> Just a thought, but in normal circumstances files *are* written to, >> even when they are just being read: the access time is updated (unless >> you mount the fs with the noatime flag). >> >=20 > quite true, but isn't that file metadata and not the actual file? I > thought most filesystems had a file-entry section, with all the > metadata, permissions, etc, and a file data section, which contains > the information of the actual file. >=20 > I guess I wouldn't be surprised if the metadata being edited were > corrupted, but to corrupt the file data/location seems odd to me. > Especially with soft updates; unless I'm mistaken, that's what it is > supposed to minimise. > -Jim But if the power failure interrupts an update, all files with data in the sector(s) it was writing are at risk. A corrupted sector can contain multiple file entries, and any or all of their entries may be lost. It is up to fsck and friends to determine which of them can still be safely accessed and restore those entries. It is not only possible, but likely that some will be lost each time this occurs. On the other hand, I thought this was one of the problems that journal led file systems were invented to solve. Bob McConnell