From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 18 Sep 2001 15:50:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 18 Sep 2001 15:50:47 -0400 Received: from mail4.svr.pol.co.uk ([195.92.193.211]:57696 "EHLO mail4.svr.pol.co.uk") by vger.kernel.org with ESMTP id ; Tue, 18 Sep 2001 15:50:32 -0400 Date: Tue, 18 Sep 2001 20:39:46 +0100 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: <20010918203946.A12814@wyvern> Reply-To: adrian.bridgett@iname.com Mail-Followup-To: Ingo Molnar , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20010916150806.E1541@turbolinux.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.3.20i From: Adrian Bridgett Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 17, 2001 at 01:16:56 +0200 (+0000), Ingo Molnar wrote: [snip] > > [...] 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. > > yes, and this is being done currently, only the primary path is used. Do you have plans to change this? I know that the SDD software for AIX load balances between paths (and I think EMC's Powerpaths do for AIX too), DMP (from Veritas) for Solaris doesn't. In fact that brings up another point - which path do you use by default? If you have the SAN situation where you have a farm of servers each with two FC cards two two FC switches and then to two ports on a storage array, you don't want everything going to the first switch. Just picking one path to use at random would be preferable (unless you want to swap every other servers cables around). One thing I know SDD does is that it doesn't use a path which has started working again until it's been working for a little while. I had a quick newbie grok through the code and couldn't see anything like that. Just an idea. Just doing a quick read I came across this comment: + * TODO: now if there are 2 multipaths in the same 2 devices, performance + * degrades dramatically because position is multipath, not device based. + * This should be changed to be device based. Also atomic sequential + * reads should be somehow balanced. shouldn't that read "more than one multipath to the same device"? I presume it's not limited to 2 multipaths? Thanks Adrian Email: adrian.bridgett@iname.com Windows NT - Unix in beta-testing. GPG/PGP keys available on public key servers Debian GNU/Linux -*- By professionals for professionals -*- www.debian.org