From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763789AbYENTLc (ORCPT ); Wed, 14 May 2008 15:11:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759064AbYENTLT (ORCPT ); Wed, 14 May 2008 15:11:19 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:39038 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753420AbYENTLR (ORCPT ); Wed, 14 May 2008 15:11:17 -0400 Message-ID: <482B394F.6070700@garzik.org> Date: Wed, 14 May 2008 15:11:11 -0400 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Sage Weil CC: Jamie Lokier , Evgeniy Polyakov , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: POHMELFS high performance network filesystem. Transactions, failover, performance. References: <20080513174523.GA1677@2ka.mipt.ru> <4829E752.8030104@garzik.org> <20080513205114.GA16489@2ka.mipt.ru> <20080514140908.GA14987@shareable.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.4 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sage Weil wrote: > On Wed, 14 May 2008, Jamie Lokier wrote: >> In that model, neighbour sensing is used to find the largest coherency >> domains fitting a set of parameters (such as "replicate datum X to N >> nodes with maximum comms latency T"). If the parameters are able to >> be met, quorum gives you the desired robustness in the event of >> node/network failures. During any time while the coherency parameters >> cannot be met, the robustness reduces to the best it can do >> temporarily, and recovers when possible later. As a bonus, you have >> some timing guarantees if they are more important. > > Anything that silently relaxes consistency like that scares me. Does > anybody really do that in practice? Well, there's Amazon Dynamo, a distributed system that places most importance on writes succeeding, if inconsistent. They choose to relax consistency up front, and on the backend absorb the cost of merging multiple versions of objects: http://www.allthingsdistributed.com/2007/10/amazons_dynamo.html (full paper) Jeff