Re: [autofs] Re: [NFS] Re: [RFC] Multiple server selection and replicated mount failover

[Peter Staubach <staubach@redhat.com>]

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 <trond.myklebust@fys.uio.no> 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