From owner-cvs-src@FreeBSD.ORG Thu Jul 22 13:45:05 2004 Return-Path: Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 015EE16A4CE; Thu, 22 Jul 2004 13:45:05 +0000 (GMT) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 5960943D2F; Thu, 22 Jul 2004 13:45:02 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from [192.168.0.201] ([192.168.0.201]) (authenticated bits=0) by pooker.samsco.org (8.12.11/8.12.10) with ESMTP id i6MDpIwl067276; Thu, 22 Jul 2004 07:51:18 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <40FFC4CD.4080706@samsco.org> Date: Thu, 22 Jul 2004 07:44:45 -0600 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7) Gecko/20040702 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Peter Jeremy References: <200407212045.i6LKjHvX090599@palm.tree.com> <40FEE569.2010209@elischer.org> <40FEE6CA.3090005@samsco.org> <20040722092441.GH3001@cirb503493.alcatel.com.au> In-Reply-To: <20040722092441.GH3001@cirb503493.alcatel.com.au> X-Enigmail-Version: 0.84.2.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, hits=0.0 required=3.8 tests=none autolearn=no version=2.63 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on pooker.samsco.org cc: cvs-src@freebsd.org cc: src-committers@freebsd.org cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/kern kern_shutdown.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 22 Jul 2004 13:45:05 -0000 Peter Jeremy wrote: > On Wed, 2004-Jul-21 15:57:30 -0600, Scott Long wrote: > >>Implementing a journalling filesystem would be a much more beneficial >>use of time here. > > > You still wind up with unwritten data in RAM, just less of it. > > How much effort would be required to add journalling to UFS or UFS2? > How big a gain does journalling give you over soft-updates? > That's a very good question. A group at RPI has been working on it for some time, but I'm not sure how close they are to having it done. If you look in the commercial world, Apple, Sun, and Wasabi/NetBSD have all done it successfully (Wasabi's isn't open source, btw). My guess is that it would take about 4-5 months to get it going, and then at least 8-12 months to ensure that there are no bugs and to tune performance. Certainly not impossible, but not something that would be production quality on short notice. I think that you would also have to make it othogonal to softupdates. The gain that you get is that your filesystem recovery time drops tremendously. You also have a much better chance of all of the metadata being on the disk and recoverable. Furthermore, it opens the door for data+metadata journalling for even more protection (at a large cost to speed and/or buffer-cache pressure, of course). Scott