From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161289AbWASJBQ (ORCPT ); Thu, 19 Jan 2006 04:01:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161293AbWASJBQ (ORCPT ); Thu, 19 Jan 2006 04:01:16 -0500 Received: from unthought.net ([212.97.129.88]:41733 "EHLO unthought.net") by vger.kernel.org with ESMTP id S1161289AbWASJBP (ORCPT ); Thu, 19 Jan 2006 04:01:15 -0500 Date: Thu, 19 Jan 2006 10:01:14 +0100 From: Jakob Oestergaard To: Neil Brown Cc: Michael Tokarev , Ross Vandegrift , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 000 of 5] md: Introduction Message-ID: <20060119090114.GF2729@unthought.net> Mail-Followup-To: Jakob Oestergaard , Neil Brown , Michael Tokarev , Ross Vandegrift , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org References: <20060117174531.27739.patches@notabene> <43CCA80B.4020603@tls.msk.ru> <20060117095019.GA27262@localhost.localdomain> <43CCD453.9070900@tls.msk.ru> <20060117160829.GA16606@lug.udel.edu> <43CD3388.9050107@tls.msk.ru> <17358.56263.806371.53617@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <17358.56263.806371.53617@cse.unsw.edu.au> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2006 at 11:22:31AM +1100, Neil Brown wrote: ... > Compare this to an offline solution (raidreconfig) where all the code > is only used occasionally. You could argue that the online version > has more code safety than the offline version.... Correct. raidreconf, however, can convert a 2 disk RAID-0 to a 4 disk RAID-5 for example - the whole design of raidreconf is fundamentally different (of course) from the on-line reshape. The on-line reshape can be (and should be) much simpler. Now, back when I wrote raidreconf, my thoughts were that md would be merged into dm, and that raidreconf should evolve into something like 'pvmove' - a user-space tool that moves blocks around, interfacing with the kernel as much as strictly necessary, allowing hot reconfiguration of RAID setups. That was the idea. Reality, however, seems to be that MD is not moving quickly into DM (for whatever reasons). Also, I haven't had the time to actually just move on this myself. Today, raidreconf is used by some, but it is not maintained, and it is often too slow for comfortable off-line usage (reconfiguration of TB sized arrays is slow - not so much because of raidreconf, but because there simply is a lot of data that needs to be moved around). I still think that putting MD into DM and extending pvmove to include raidreconf functionality, would be the way to go. The final solution should also be tolerant (like pvmove is today) of power cycles during reconfiguration - the operation should be re-startable. Anyway - this is just me dreaming - I don't have time to do this and it seems that currently noone else has either. Great initiative with the reshape Neil - hot reconfiguration is much needed - personally I still hope to see MD move into DM and pvmove including raidreconf functionality, but I guess that when we're eating an elephant we should be satisfied with taking one bite at a time :) -- / jakob