From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 2 May 2002 12:38:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 2 May 2002 12:38:00 -0400 Received: from unthought.net ([212.97.129.24]:28307 "HELO mail.unthought.net") by vger.kernel.org with SMTP id ; Thu, 2 May 2002 12:37:59 -0400 Date: Thu, 2 May 2002 18:37:58 +0200 From: =?iso-8859-1?Q?Jakob_=D8stergaard?= To: Bernd Eckenfels Cc: linux-kernel@vger.kernel.org Subject: Re: raid1 performance Message-ID: <20020502183758.Q31556@unthought.net> Mail-Followup-To: =?iso-8859-1?Q?Jakob_=D8stergaard?= , Bernd Eckenfels , linux-kernel@vger.kernel.org In-Reply-To: <20020501130127.A10936@borg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit User-Agent: Mutt/1.2i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 01, 2002 at 11:23:23PM +0200, Bernd Eckenfels wrote: > In article <20020501130127.A10936@borg.org> you wrote: > > 1. Does the OS even know where the heads are in a modern IDE disk? > > > 2. Is "closer" any more finely grained than a binary > > positioned/not-positioned? > > > And I guess another question: How much does RAID 1 help and under what > > kinds of usage? > > No, you just distribute the ready round robin, this means each disk has only > half the seeks it had before. No, this is the way it was done a long time ago. It turns out to be an incredibly bad idea. In fact, it is the most CPU-efficient way of guaranteeing the largest average seek times on your disks ;) The RAID-1 code now looks at which disk worked closest to the wanted position last, and picks that disk for the seek. > As long as you do not spread continous blocks > (readahead) stats are good you actually reduce overall seeks. This helps > actually even if no seek is involved because of the fact that you need to > wait for the begin of a track to read it. The "new" code (which is not that new anymore) will allow one disk to keep on a single sequential read for a long time (eventually it will kick in the idle disk(s) though). -- ................................................................ : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob Østergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: