From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: POHMELFS high performance network filesystem. Transactions, failover, performance. Date: Wed, 14 May 2008 17:49:35 -0400 Message-ID: <482B5E6F.4020204@garzik.org> References: <20080513174523.GA1677@2ka.mipt.ru> <4829E752.8030104@garzik.org> <20080513205114.GA16489@2ka.mipt.ru> <482B2E50.2030601@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Evgeniy Polyakov , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Sage Weil Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:52546 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbYENVti (ORCPT ); Wed, 14 May 2008 17:49:38 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Sage Weil wrote: > You mean if, say, some verifiable metadata or a trusted third party stores > that checksum? Sure. This is just pushing the what-has-committed Yes. > information to some other party, though, who will presumably face the same > problem of requiring a majority for verifiable correctness. This is more > or less what most people do in practice... using Paxos for critical state > and piggybacking the rest of the system's consistency off of that. More like receiving a guarantee of consensus (just like any signature on data), while only needing to be able to communicate with a single node. >>> (This is why Paxos is typically used only for critical cluster >>> configuration/state, not regular data.) >> Yep, I'm working on a config daemon a la Chubby or zookeeper, based on Paxos, >> that does just this. :) > > Cool. Do you have a URL? I'd be interested in seeing how you diverge > from classic paxos. For Ceph's monitor daemon, the main requirements > (besides strict correctness guarantees) were scalable (distributed) read > access, and a history of state changes. Nothing too unusual. Is there a URL? Yes. http://linux.yyz.us/projects/cld.html It it useful? No. It's just a skeleton code right now. I am experimenting with various Paxos algorithms as we speak, which is why it's fresh in my mind at the moment. I also forgot to mention hyperspace, which is another up-and-coming player in this area, alongside Chubby and zookeeper. Jeff