From owner-freebsd-current@FreeBSD.ORG Tue Oct 19 20:20:56 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A94B516A4CE for ; Tue, 19 Oct 2004 20:20:56 +0000 (GMT) Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by mx1.FreeBSD.org (Postfix) with ESMTP id 3EB8043D49 for ; Tue, 19 Oct 2004 20:20:56 +0000 (GMT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.12.11/8.12.11) id i9JKKlIN009503; Tue, 19 Oct 2004 15:20:47 -0500 (CDT) (envelope-from dan) Date: Tue, 19 Oct 2004 15:20:47 -0500 From: Dan Nelson To: Ryan Sommers Message-ID: <20041019202047.GB83510@dan.emsphone.com> References: <417538B9.7070001@club-internet.fr> <41755FAF.8080300@colleduc.ee> <53515.208.4.77.15.1098213002.squirrel@208.4.77.15> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53515.208.4.77.15.1098213002.squirrel@208.4.77.15> X-OS: FreeBSD 5.3-BETA7 X-message-flag: Outlook Error User-Agent: Mutt/1.5.6i cc: =?utf-8?Q?Jean-S=C3=A9bastien_P=C3=A9dron?= cc: Kalev Lember cc: freebsd-current@freebsd.org Subject: Re: Read-only ReiserFS support for FreeBSD 5.x X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Oct 2004 20:20:56 -0000 In the last episode (Oct 19), Ryan Sommers said: > It is my understanding that SoftUpdates offers the same guarantees > that journaling does. It ensures file-system consistancy even in the > event of system failure. I believe the only reason fsck is still run > is to clean up the few cases that SoftUpdates can't detect, which is > just block bitmaps and inode link counts. Neither of these are > critical in that they can both be performed by a background fsck on a > snapshot of a live filesystem. Softupdates guarantees only that the filesystem will be in a consistent state. That state may be missing directories created up to kern.dirdelay seconds ago, files created up to kern.filedelay seconds ago, and metadata changed up to kern.metadelay seconds ago. I recommend cranking down all three values to under 10 seconds if you are worried about losing recently-modified files after a crash. Journalled filesystems may guarantee that the filesystem will be consistent to a particular point in time, so if your editor updates (for example) rc.conf by creating a new copy named rc.conf.new, deleting rc.conf, then renaming the copy to rc.conf, you are guaranteed that either rc.conf or rc.conf.new will be in the filessytem after a crash. With softupdates, you may lose both files. I don't know if current journalled fses actually journal all writes like this (as opposed to just journalling what the OS decides to flush out of its cache), but they are much less likely to lose files the way softupdates can. -- Dan Nelson dnelson@allantgroup.com