From: Ric Wheeler Subject: Re: ext3 default journal mode Date: Mon, 20 Jul 2009 17:33:02 -0400 Message-ID: <4A64E28E.2000907@redhat.com> References: <4A63DB89.2060306@redhat.com> <20090720212904.GI2416@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "linux-ext4@vger.kernel.org" , Valerie Aurora , "Stephen C. Tweedie" , Eric Sandeen , Andreas Dilger , Chris Mason , Josef Bacik , Mingming Cao To: Theodore Tso Return-path: Received: from mx2.redhat.com ([66.187.237.31]:40352 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751402AbZGTVdT (ORCPT ); Mon, 20 Jul 2009 17:33:19 -0400 In-Reply-To: <20090720212904.GI2416@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 07/20/2009 05:29 PM, Theodore Tso wrote: > Here's a revised proposal for the KCONFIG text. > > Hopefully this is balanced about the two sides of the issue, without > explicitly advocating for one choice versus another. > > What do people think? > > - Ted Hi Ted, I think that this is a huge improvement - thanks! Ric > > P.S. Note that date=writeback does not make the filesystem more > "prone to corruption after crashes". > > > config EXT3_DEFAULTS_TO_ORDERED > bool "Default to 'data=ordered' in ext3" > depends on EXT3_FS > help > If a filesystem does not explicitly specify a data ordering > mode, and the journal capability allowed it, ext3 used to > historically default to 'data=ordered'. > > Data=ordered mode is the mode used by most distributions, but can > introduce latency problems in some workloads, especially if there > is a combination of high bandwidth background writes and foreground > processes calling fsync() and waiting for the result. In worst > case scenarios, the fsync() call can 500ms to multiple seconds > to return. > > The problem with using a default of data=writeback, however, > is that is that after a system crash or a power failure, > files that were written right before the system went down > could contain previously written data or other garbage. > With data=ordered mode, any blocks in the file will have > been data written by the application, avoiding a possibility > of a security breach, which is especially problematic on a > multi-user system. Note, however, that data=ordered does > not guarantee that the file will be consistent at an > application level; the application must use fsync() at > appropriate commit points in order to guarantee > application-level consistency. > > If you have been historically happy with ext3's performance, > data=ordered mode will be a safe choice and you should > answer "y" here. If you understand the reliability and data > privacy issues of data=writeback and are willing to make > that trade off, answer "n". >