Re: [nfsv4] Review comments for WGLC of draft-ietf-nfsv4-layout-types

Christoph Hellwig <> Wed, 16 August 2017 09:04 UTC

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Date: Wed, 16 Aug 2017 11:04:44 +0200
From: Christoph Hellwig <>
To: Chuck Lever <>
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Subject: Re: [nfsv4] Review comments for WGLC of draft-ietf-nfsv4-layout-types
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I don't have a whole lot of time to spare, so this is a very
narrow review with the focus on interactions with the scsi
and rdma layout types.

The first thing I noticed is that section 3 claims:

"There have been no published specifications for control protocols as yet."

which I don't think is true any more.  The SCSI layout fully specifies
the interaction between the MDS and the storage device, so it should
be considered to include a control protocol.

Note that in terms of specifications the it only uses SCSI and thus
the storage protocol, but it uses different features in the SCSI
specifications that are designed to be a control protocol, and the
particular way in the MDS has to use SCSI persistent reservations
could be considered a protocol by itself.  So the paragraph below
about loose coupling doesn't really apply in this case either.

All of that is pretty editorial though as it doesn't change any of
the fundamentals of the section.

I'm not sure what the point of

"Whether the metadata server allows access over other protocols
 (e.g., NFSv3, Server Message Block (SMB), etc) is strictly an
 implementation choice, just as it is in the case of any other
 (i.e., non-pNFS-supporting) NFSv4.1 server."

is.  While the statement is true nothing in NFS talks about
cross-protocol access to servers, so I don't think it matters.

Section 4.1 probably needs an update to include the SCSI layout
given that it claims to document the existing layout types.  The
block layout section is more or less valid for the SCSI layout
as well, so I would suggest to handle the SCSI layout in the
same section.

Another aspect that might be worth mentioning somewhere is
that layouts may revoke access to the whole storage device
for fencing when a layout recall is not acted upon.