From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: "Enhanced" MD code avaible for review Date: Thu, 25 Mar 2004 19:13:36 -0500 Sender: linux-raid-owner@vger.kernel.org Message-ID: <406375B0.5040406@pobox.com> References: <760890000.1079727553@aslan.btc.adaptec.com> <16480.61927.863086.637055@notabene.cse.unsw.edu.au> <40624235.30108@pobox.com> <200403251200.35199.kevcorry@us.ibm.com> <40632804.1020101@pobox.com> <1030470000.1080257746@aslan.btc.adaptec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1030470000.1080257746@aslan.btc.adaptec.com> To: "Justin T. Gibbs" Cc: Kevin Corry , linux-kernel@vger.kernel.org, Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Justin T. Gibbs wrote: >>I respectfully disagree with the EMD folks that a userland approach is >>impossible, given all the failure scenarios. > > > I've never said that it was impossible, just unwise. I believe > that a userland approach offers no benefit over allowing the kernel > to perform all meta-data operations. The end result of such an > approach (given feature and robustness parity with the EMD solution) > is a larger resident side, code duplication, and more complicated > configuration/management interfaces. There is some code duplication, yes. But the right userspace solution does not have a larger RSS, and has _less_ complicated management interfaces. A key benefit of "do it in userland" is a clear gain in flexibility, simplicity, and debuggability (if that's a word). But it's hard. It requires some deep thinking. It's a whole lot easier to do everything in the kernel -- but that doesn't offer you the protections of userland, particularly separate address spaces from the kernel, and having to try harder to crash the kernel. :) Jeff