From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261881AbTJRWz3 (ORCPT ); Sat, 18 Oct 2003 18:55:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261893AbTJRWz2 (ORCPT ); Sat, 18 Oct 2003 18:55:28 -0400 Received: from vladimir.pegasys.ws ([64.220.160.58]:54280 "EHLO vladimir.pegasys.ws") by vger.kernel.org with ESMTP id S261881AbTJRWz1 (ORCPT ); Sat, 18 Oct 2003 18:55:27 -0400 Date: Sat, 18 Oct 2003 15:55:21 -0700 From: jw schultz To: linux-kernel@vger.kernel.org Subject: Re: Software RAID5 with 2.6.0-test Message-ID: <20031018225521.GA3699@pegasys.ws> Mail-Followup-To: jw schultz , linux-kernel@vger.kernel.org References: <1065690658.10389.19.camel@slurv> <3F903768.7060803@rackable.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.3.27i X-Message-Flag: This message may contain content offensive to Atheists and servants of false gods. Read at your own risk. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 17, 2003 at 09:18:24PM +0200, Måns Rullgård wrote: > Samuel Flory writes: > > >> What about the RAID controllers in the $400 category? Surely, they > >> must be doing something better than the $50 fakeraid controllers. > >> > > > > Yes, but follow this logic. > > > > 1)You are willing to devote 10% of 2Ghz xeon to software raid. > > 2)A $500+ controller has a 100Mhz proccessor. > > > > Thus just from this you could guess that software raid has x2 as > > many clock cycles availble to it. It's even worse when you realize > > the 2Ghz xeon is a better proccessor in many more ways than just > > clock cycles. > > How about this logic: > > 1) If the processor on the RAID controller can handle the full > bandwidth of the disks, it's fast enough. > 2) If someone else does the 10% work, the CPU can do 10% more work. And as has been addressed on this list before: 3) If the additional I/O traffic of the RAID can be kept off of the system busses the overall system throughput goes up. Once the CPU reaches a certain level of performance it is the I/O and memory that limit things. Do you really want to pollute L1 cache with RAID-5? When the $400 RAID server card can saturate the PCI buss it doesn't matter how much spare CPU you have, SW RAID will not be able to match the performance. -- ________________________________________________________________ J.W. Schultz Pegasystems Technologies email address: jw@pegasys.ws Remember Cernan and Schmitt