From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992823AbXCIA6I (ORCPT ); Thu, 8 Mar 2007 19:58:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2992824AbXCIA6I (ORCPT ); Thu, 8 Mar 2007 19:58:08 -0500 Received: from web52507.mail.yahoo.com ([206.190.48.190]:45941 "HELO web52507.mail.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S2992823AbXCIA6G (ORCPT ); Thu, 8 Mar 2007 19:58:06 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=szdt3N9FzXUAjY0775upFi+3iVtKdloAVJxQqPX5GwlDIKOwDrOwo+z5WObg/Cc4udTut2szrwmCXH0G9J9YqEWYhgmhq9OsOqv50zh2qaKGz0jBDM0t2+akAa9x4qLnk7/KSUlqINsGCPRSK+ERCNc6LLZ90Y6q62iubarLewE=; X-YMail-OSG: 0oa8ixEVM1m6JMJgDHMduDzYqutSBcXwewdd7vX8Y0QXupVS2vu3Ksc0ks1OylJxlE_HRFEySkR5KVCYk_T5hh0lKohMpXgQuztowLME6zF.uyaub9r9RrP.M893DjBSFgsg_ZyLFArHvO0h0oTVGR9kqXRc_D5sVhsUHUl_gAVUrp4mQjR3 Date: Thu, 8 Mar 2007 16:58:03 -0800 (PST) From: Marc Perkel Subject: Re: Raid 10 Problems? To: Michael Tokarev , Jan Engelhardt Cc: dean gaudet , Marc Perkel , Linux Kernel Mailing List , linux-raid@vger.kernel.org In-Reply-To: <45F09698.7090606@tls.msk.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Message-ID: <464915.77231.qm@web52507.mail.yahoo.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --- Michael Tokarev wrote: > Jan Engelhardt wrote: > [] > > The other thing is, the bitmap is supposed to be > written out at intervals, > > not at every write, so the extra head movement for > bitmap updates should > > be really low, and not making the tar -xjf process > slower by half a minute. > > Is there a way to tweak the write-bitmap-to-disk > interval? Perhaps > > something in /sys or ye olde /proc. Maybe > linux-raid@ knows 8) > > Hmm. Bitmap is supposed to be written before actual > data write, to mark > the to-be-written areas of the array as "being > written", so that those > areas can be detected and recovered in case of power > failure during > actual write. > > So in case of writing to a clean array, head > movement always takes place - > first got to bitmap area, and second to the actual > data area. > > That "written at intervals" is about clearing the > bitmaps after some idle > time. > > In other words, dirtying bitmap bits occurs right > before actual write, > and clearing bits occurs at intervals. > > Sure, if you write to (or near) the same place again > and again, without > giving a chance to md subsystem to actually clean > the bitmap, there will > be no additional head movement. And that means, for > example, tar -xjf > sometimes, since filesystem will place the files > being extracted close to > each other, thus hitting the same bit in the bitmap, > hence md will skip > repeated bitmap updates in this case. > > /mjt > I assume that if a block is already dirty then that is cached somewhere in memory so you aren't writing to the bitmap unless you're changing it for clean to dirty? If that's the case then I would think that writing to the map wouldn't be that expensive? ____________________________________________________________________________________ Now that's room service! Choose from over 150,000 hotels in 45,000 destinations on Yahoo! Travel to find your fit. http://farechase.yahoo.com/promo-generic-14795097