Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755147AbXFULAr (ORCPT ); Thu, 21 Jun 2007 07:00:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753508AbXFULAh (ORCPT ); Thu, 21 Jun 2007 07:00:37 -0400 Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:35849 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752697AbXFULAg (ORCPT ); Thu, 21 Jun 2007 07:00:36 -0400 Date: Thu, 21 Jun 2007 21:00:12 +1000 From: David Chinner To: David Chinner Cc: Neil Brown , Avi Kivity , david@lang.hm, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: limits on raid Message-ID: <20070621110006.GU85884050@sgi.com> References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <467273AB.9010202@argo.co.il> <18035.3009.568832.785308@notabene.brown> <20070618045759.GD85884050@sgi.com> <18041.59628.370832.633244@notabene.brown> <20070621063936.GT85884050@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070621063936.GT85884050@sgi.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1763 Lines: 43 On Thu, Jun 21, 2007 at 04:39:36PM +1000, David Chinner wrote: > FWIW, I don't think this really removes the need for a filesystem to > be able to keep multiple copies of stuff about. If the copy(s) on a > device are gone, you've still got to have another copy somewhere > else to get it back... Speaking of knowing where you can safely put multiple copies, I'm in the process of telling XFS about linear alignment of the underlying array so that we can: - spread out the load across it faster. - provide workload isolation - know where *not* to put duplicate or EDAC data I'm aiming at identical subvolumes so it's simple to implement. All I need to know is the size of each subvolume. I can supply that at mkfs time or in a mount option, but I want something that can works automatically so I need to query dm to find out the size of each underlying device during mount. We should also pass stripe unit/width with the same interface while we are at it... What's the correct and safe way to get this information from dm both into the kernel and out to userspace (mkfs)? FWIW, my end goal is to be able to map the underlying block device address spaces directly into the filesystem so that the filesystem is able to use the underlying devices intelligently and I can logically separate caches and writeback for the separate subdevices. A struct address_space per subdevice would be ideal - anyone got ideas on how to get that? Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/