From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 16 Sep 2001 17:08:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 16 Sep 2001 17:08:28 -0400 Received: from h24-64-71-161.cg.shawcable.net ([24.64.71.161]:29686 "EHLO webber.adilger.int") by vger.kernel.org with ESMTP id ; Sun, 16 Sep 2001 17:08:10 -0400 From: Andreas Dilger Date: Sun, 16 Sep 2001 15:08:06 -0600 To: Ingo Molnar Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch] multipath RAID personality, 2.4.10-pre9 Message-ID: <20010916150806.E1541@turbolinux.com> Mail-Followup-To: Ingo Molnar , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.3.20i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sep 14, 2001 12:01 +0200, Ingo Molnar wrote: > the attached patches implement multipath IO for Linux in form of a sw-RAID > personality. Multipath-IO is the ability of certain devices to address the > same physical disk over multiple 'IO paths'. > /* > * This routine returns the disk from which the requested read should > * be done. It bookkeeps the last read position for every disk > * in array and when new read requests come, the disk which last > * position is nearest to the request, is chosen. I'm not sure I understand why this is here? If we are talking about a multipath situation, there IS only a single disk, so which path is chosen is mostly irrelevant. Also, it is my understanding that with some multipath hardware, if you read from the "backup" path it will kill access to the primary path (this can be used when more than one system access shared disk for failover). As a result, we should always read from the "primary" path for each disk unless there is an error. Cheers, Andreas -- Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto, \ would they cancel out, leaving him still hungry?" http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert