Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S947045AbXHMPFs (ORCPT ); Mon, 13 Aug 2007 11:05:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S972336AbXHMMoE (ORCPT ); Mon, 13 Aug 2007 08:44:04 -0400 Received: from s2.ukfsn.org ([217.158.120.143]:52200 "EHLO mail.ukfsn.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753904AbXHMMn7 (ORCPT ); Mon, 13 Aug 2007 08:43:59 -0400 Message-ID: <46C0520B.20804@dgreaves.com> Date: Mon, 13 Aug 2007 13:43:55 +0100 From: David Greaves User-Agent: Mozilla-Thunderbird 2.0.0.4 (X11/20070618) MIME-Version: 1.0 To: david@lang.hm Cc: Paul Clements , Jan Engelhardt , Al Boldi , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: [RFD] Layering: Use-Case Composers (was: DRBD - what is it, anyways? [compare with e.g. NBD + MD raid]) References: <200708121335.17267.a1426z@gawab.com> <20070812174549.GA2915@teal.hq.k1024.org> <46BFB6BB.80406@steeleye.com> <46C01052.4050708@dgreaves.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1668 Lines: 35 david@lang.hm wrote: >> Would this just be relevant to network devices or would it improve >> support for jostled usb and sata hot-plugging I wonder? > > good question, I suspect that some of the error handling would be > similar (for devices that are unreachable not haning the system for > example), but a lot of the rest would be different (do you really want > to try to auto-resync to a drive that you _think_ just reappeared, Well, omit 'think' and the answer may be "yes". A lot of systems are quite simple and RAID is common on the desktop now. If jostled USB fits into this category - then "yes". > what > if it's a different drive? how can you be sure? And that's the key isn't it. We have the RAID device UUID and the superblock info. Isn't that enough? If not then given the work involved an extended superblock wouldn't be unreasonable. And I suspect the capability of devices would need recording in the superblock too? eg 'retry-on-fail' I can see how md would fail a device but may now periodically retry it. If a retry shows that it's back then it would validate it (UUID) and then resync it. > ) the error rate of a > network is gong to be significantly higher then for USB or SATA drives > (although I suppose iscsi would be limilar) I do agree - I was looking for value-add for the existing subsystem. If this benefits existing RAID users then it's more likely to be attractive. David - 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/