From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Greaves Subject: Re: [RFD] Layering: Use-Case Composers (was: DRBD - what is it, anyways? [compare with e.g. NBD + MD raid]) Date: Mon, 13 Aug 2007 09:03:30 +0100 Message-ID: <46C01052.4050708@dgreaves.com> References: <200708121335.17267.a1426z@gawab.com> <20070812174549.GA2915@teal.hq.k1024.org> <46BFB6BB.80406@steeleye.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 To: david@lang.hm Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org david@lang.hm wrote: > per the message below MD (or DM) would need to be modified to work > reasonably well with one of the disk components being over an unreliable > link (like a network link) > > are the MD/DM maintainers interested in extending their code in this > direction? or would they prefer to keep it simpler by being able to > continue to assume that the raid components are connected over a highly > reliable connection? > > if they are interested in adding (and maintaining) this functionality > then there is a real possibility that NBD+MD/DM could eliminate the need > for DRDB. however if they are not interested in adding all the code to > deal with the network type issues, then the argument that DRDB should > not be merged becouse you can do the same thing with MD/DM + NBD is > invalid and can be dropped/ignored > > David Lang As a user I'd like to see md/nbd be extended to cope with unreliable links. I think md could be better in handling link exceptions. My unreliable memory recalls sporadic issues with hot-plug leaving md hanging and certain lower level errors (or even very high latency) causing unsatisfactory behaviour in what is supposed to be a fault 'tolerant' subsystem. Would this just be relevant to network devices or would it improve support for jostled usb and sata hot-plugging I wonder? David