From: Peter Staubach Subject: Re: [autofs] Re: [NFS] Re: [RFC] Multiple server selection and replicated mount failover Date: Wed, 24 May 2006 15:17:03 -0400 Message-ID: <4474B12F.5060706@redhat.com> References: <1148488156.5872.42.camel@lade.trondhjem.org> <1148495501.11732.8.camel@lade.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Jeff Moyer , Ian Kent , linux-fsdevel , autofs mailing list , nfs@lists.sourceforge.net Return-path: To: Trond Myklebust In-Reply-To: <1148495501.11732.8.camel@lade.trondhjem.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Trond Myklebust wrote: >On Wed, 2006-05-24 at 13:58 -0400, Jeff Moyer wrote: > > >>==> Regarding [autofs] Re: [NFS] Re: [RFC] Multiple server selection and replicated mount failover; Trond Myklebust adds: >> >>trond.myklebust> On Wed, 2006-05-24 at 13:05 +0800, Ian Kent wrote: >> >> >>>>>4) How does NFS v4 fit into this picture as I believe that some >>>>> of this functionality is included within the protocol. >>>>> >>>>> >>>>And this. >>>> >>>>NFS v4 appears quite different so should I be considering this for v2 and >>>>v3 only? >>>> >>>> >>trond.myklebust> NFSv4 has full support for migration/replication in the >>trond.myklebust> protocol. If a filesystem fails on a given server, then >>trond.myklebust> the server itself will tell the client where it can find >>trond.myklebust> the replicas. There should be no need to provide that >>trond.myklebust> information at mount time. >> >>And what happens when the server disappears? >> >> > >There are 2 strategies for dealing with that: > >Firstly, we can maintain a cache of the list of replica volumes (we can >request the list of replicas when we mount the original volume). > > > This assumes a lot on the part of the server and it doesn't seem to me that current server implementations are ready with the infrastructure to be able to make this a reality. I think that the client should be prepared to handle this sort of scenario but also be prepared to take a list of servers at mount time too. >Secondly, there are plans to add a backup list of failover servers in a >specialised DNS record. This strategy could be made to work for NFSv2/v3 >too. > This would seem to be a solution for how to determine the list of replicas, but not how the NFS client fails over from one replica to the next. Thanx... ps