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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Thu, 21 Mar 2019 08:49:27 -0400
Message-ID: <CAN-5tyFPCLWY0J0PftdOHuA2FAYGL7VaQYdj-Xu5dQXudU=PwQ@mail.gmail.com>
Subject: Re: Some questions about Trunking
To:     Marvin Zhang <fanzier@gmail.com>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
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On Wed, Mar 20, 2019 at 11:05 PM Marvin Zhang <fanzier@gmail.com> wrote:
>
> 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.

There was a series of patches proposed by Trond about 2 years ago that
add "nconnect=X" mount option that will create X TCP connections to
the server. You can find that series apply it and build a kernel with
that or you can use SLES15 distro where those patches were included.


>
> >
> > 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.