NFS4 Information from the University of Michigan

NFSv4 information can be found from the University of Michigan Centre for Information Technology Integration Project NFS Version 4 Open Source Refrence Implementation

I like the rfc3530 definition of NFS v4 definition as written in the site

The Network File System (NFS) version 4 is a distributed filesystem protocol which owes heritage to NFS protocol version 2, RFC 1094, and version 3, RFC 1813. Unlike earlier versions, the NFS version 4 protocol supports traditional file access while integrating support for file locking and the mount protocol. In addition, support for strong security (and its negotiation), compound operations, client caching, and internationalization have been added. Of course, attention has been applied to making NFS version 4 operate well in an Internet environment. 

 Interesting  and relevant information

1. NFSv4 wiki
   (Includes information on 4.1, pNFS prototype)
2. Connectathon Test Suite
3. General troubleshooting recommendations
4. Performance and Stress tests for NFS