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Re: [nfsv4] pNFS file and use of RPC-over-RDMA to access an NFSv4.1 data server

Tom Talpey <tom@talpey.com> Thu, 26 April 2018 12:23 UTC

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From: Tom Talpey <tom@talpey.com>
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Date: Thu, 26 Apr 2018 08:23:31 -0400
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Subject: Re: [nfsv4] pNFS file and use of RPC-over-RDMA to access an NFSv4.1 data server
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On 4/25/2018 3:30 PM, Chuck Lever wrote:
> NFSv4.1 has a "gear shift" capability where, after establishment
> of a TCP connection, the client and server detect that an RDMA
> connection is possible. At this point, I'm not aware of any
> implementation of this capability. Are we as a community deciding
> to abandon this approach for NFS?

I hope not! Note, the iSCSI/RDMA mapping, iSER, has a similar
capability in its "RDMAExtensions" key at logon.

But there are some challenges. RoCE and InfiniBand only support an
RDMA connection, and can't perform the step-up. And while the iWARP
(specifically, MPAv2) protocol does, the local APIs to drive the shift
are immature.

I believe the iSER and NFS/RDMA communities could work together to
enable this type of interaction. But as you point out, these are
implementation questions. The protocols are in place.

Tom.

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