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From:   Marvin Zhang <fanzier@gmail.com>
Date:   Thu, 21 Mar 2019 11:04:42 +0800
Message-ID: <CA+5eE-QZ5J5jjSvGUGj8pOHNwZfHpFnyoQd0QanqOEGLW5LpcA@mail.gmail.com>
Subject: Re: Some questions about Trunking
To:     Olga Kornievskaia <aglo@umich.edu>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
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On Wed, Mar 20, 2019 at 10:29 PM Olga Kornievskaia <aglo@umich.edu> wrote:
>
> This question is more of an NFSv4.1 protocol question thus I would
> encourage you to ask it on the nfsv4@ietf.org.
>
> On Tue, Mar 19, 2019 at 11:06 PM Marvin Zhang <fanzier@gmail.com> wrote:
> >
> > Hi Experts,
> > Here are some questions about trunking:
> > 1.  For session trunking. During first mount(or first connection),
> > client create a session. During the second mount(or second
> > connection), client will reuse the session which the first connection
> > created. Does the second mount create a new super block or reuse the
> > previous?
> > If there is a READ request on this session, how to judge to
> > use which connection?
>
> Session trunking does not require the client to create a different
> mount in your example. A single mount could have multiple TCP
> connections established between a client and a server and they would
> use the same NFSv4.1 session to send operations to the server. A read
> operation issued by the application using the NFS mount could use one
> of those connection and the question which one it would use is
> protocol implementation specific. Simplest implementation round robins
> connections for incoming RPC tasks.
I just followed this article:
https://packetpushers.net/multipathing-nfs4-1-kvm/ . In this article,
client mounts the server twice in differ conections. But as you said,
it's not session trunking. I still don't konw how to mount a server
only once with two connection. Could you give me a sample here? I
don't find any example in google searching result.

>
> If the client mounted a server and then decides to mount the same
> server again (given same mount options and credentials), in the linux
> implementation, the existing NFS client (and its TCP connection) would
> be re-used. Thus it would not be a case of session trunking.
>
> > 2. For client id truking. As protocol said, client can create multipl
> > session at the same time. I can't understand in which scenario client
> > can create multiple session
>
> Again IETF list can provide some examples and motivations for the
> clientid case. I think perhaps it was for the clustered server
> environment where the client would use the same client id across
> different cluster nodes but it would establish unique sessions to the
> nodes.