From: Pavel Machek Subject: Re: [testcase] test your fs/storage stack (was Re: [patch] ext2/3: document conditions when reliable operation is possible) Date: Sat, 5 Sep 2009 12:28:10 +0200 Message-ID: <20090905102810.GA1341@ucw.cz> References: <20090826001645.GN4300@elf.ucw.cz> <200909022141.48827.rob@landley.net> <4A9FCF53.10105@hp.com> <200909040244.54772.rob@landley.net> <4AA0FECE.3010200@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Rob Landley , jim owens , david@lang.hm, Theodore Tso , Florian Weimer , Goswin von Brederlow , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net To: Ric Wheeler Return-path: Content-Disposition: inline In-Reply-To: <4AA0FECE.3010200@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Fri 2009-09-04 07:49:34, Ric Wheeler wrote: > On 09/04/2009 03:44 AM, Rob Landley wrote: >> On Thursday 03 September 2009 09:14:43 jim owens wrote: >> >>> Rob Landley wrote: >>> >>>> I think he understands he was clueless too, that's why he investigated >>>> the failure and wrote it up for posterity. >>>> >>>> >>>>> And Ric said do not stigmatize whole classes of A) devices, B) raid, >>>>> and C) filesystems with "Pavel says...". >>>>> >>>> I don't care what "Pavel says", so you can leave the ad hominem at the >>>> door, thanks. >>>> >>> See, this is exactly the problem we have with all the proposed >>> documentation. The reader (you) did not get what the writer (me) >>> was trying to say. That does not say either of us was wrong in >>> what we thought was meant, simply that we did not communicate. >>> >> That's why I've mostly stopped bothering with this thread. I could respond to >> Ric Wheeler's latest (what does write barriers have to do with whether or not >> a multi-sector stripe is guaranteed to be atomically updated during a panic or >> power failure?) but there's just no point. >> > > The point of that post was that the failure that you and Pavel both > attribute to RAID and journalled fs happens whenever the storage cannot > promise to do atomic writes of a logical FS block (prevent torn > pages/split writes/etc). I gave a specific example of why this happens > even with simple, single disk systems. ext3 does not expect atomic write of 4K block, according to Ted. So no, it is not broken on single disk. >> The LWN article on the topic is out, and incomplete as it is I expect it's the >> best documentation anybody will actually _read_. Would anyone (probably privately?) share the lwn link? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html