Return-Path: Received: from fieldses.org ([174.143.236.118]:47061 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757825Ab0LNTPR (ORCPT ); Tue, 14 Dec 2010 14:15:17 -0500 Date: Tue, 14 Dec 2010 14:15:14 -0500 From: "J. Bruce Fields" To: DENIEL Philippe Cc: Thomas Haynes , linux-nfs@vger.kernel.org Subject: Re: Side effects of having NFSv4 mounted over udp Message-ID: <20101214191514.GC24828@fieldses.org> References: <4D05CF50.1010305@cea.fr> <20101213191634.GB2230@fieldses.org> <4D071E32.905@cea.fr> Content-Type: text/plain; charset=us-ascii In-Reply-To: <4D071E32.905@cea.fr> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Tue, Dec 14, 2010 at 08:35:14AM +0100, DENIEL Philippe wrote: > Hi > >The Linux server allows it, but I've been considering that a > >(low-priority) bug, so it wouldn't be safe to assume it will continue > >working. > I am mostly thinking at the client side using as well udp and tcp. > Would the "NFSv4 client over UDP" behaves differently then the same > client over TCP ? > > >That aside, if you have a perfect network, > I can trust my network. It's not a WAN, it's located into a very > massive cluster (it's kind of "internal LAN"). It's a very high > throughput network (IB based) so I believe there are less "hardware > based reason" to loose packets. > > >NFSv4.0 at least will > >probably work. > OK. > >(Not 4.1 since backchannel setup will fail?) > What is erroneous in using UDP for NFSv4.1 backchannels ? I assumed it would require some stronger notion of a "connection" than UDP could provide. But maybe it could be made to work somehow. > >Are you really sure that you can't make tcp scale to thousands of > >clients? > I am a bit afraid of a "No more file descriptors" effect. If I have > one TCP socket per client and thousands of clients, I have less > remaining fds for other purposes. Another point : UDP is a "cheap" > protocol. I can have bunches of clients without overloading the > server (a new client will almost cost nothing to the server, just > the cost of a new clientid negotiation) . Is the tcp state all that much more? > I was wondering if it > could be reliable to use it for NFSv4 inside a large cluster. Well, it'd require some spec changes in any case. --b.