From: Theodore Tso Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Mon, 24 Aug 2009 09:50:35 -0400 Message-ID: <20090824135035.GI23677@mit.edu> References: <20090312092114.GC6949@elf.ucw.cz> <200903121413.04434.rob@landley.net> <20090316122847.GI2405@elf.ucw.cz> <200903161426.24904.rob@landley.net> <20090323104525.GA17969@elf.ucw.cz> <87ljqn82zc.fsf@frosties.localdomain> <20090824093143.GD25591@elf.ucw.cz> <82k50tjw7u.fsf@mid.bfk.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Pavel Machek , Goswin von Brederlow , Rob Landley , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org To: Florian Weimer Return-path: Content-Disposition: inline In-Reply-To: <82k50tjw7u.fsf@mid.bfk.de> Sender: linux-doc-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, Aug 24, 2009 at 11:19:01AM +0000, Florian Weimer wrote: > > +* don't damage the old data on a failed write (ATOMIC-WRITES) > > + > > + (Thrash may get written into sectors during powerfail. And > > + ext3 handles this surprisingly well at least in the > > + catastrophic case of garbage getting written into the inode > > + table, since the journal replay often will "repair" the > > + garbage that was written into the filesystem metadata blocks. > > Isn't this by design? In other words, if the metadata doesn't survive > non-atomic writes, wouldn't it be an ext3 bug? So I got confused when I quoted your note, which I had assumed was exactly what Pavel had written in his documentation. In fact, what he had written was this: +Don't damage the old data on a failed write (ATOMIC-WRITES) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Either whole sector is correctly written or nothing is written during +powerfail. + +.... So he had explicitly stated that he only cared about the whole sector being written (or not written) in the power fail case, and not any other. I'd suggest changing ATOMIC-WRITES to ATOMIC-WRITE-ON-POWERFAIL, since the one-line summary, "Don't damage the old data on a failed write", is also singularly misleading. - Ted