From Linux NFS
rfc 5661 includes protocol for directory delegations, but implementation efforts are currently stalled; see NFSv4.1 Directory Delegations for experience from an early CITI prototyping effort.
server IPv6 support is now completed.
Core NFSv4.1 support should be up to spec at this point; see Server 4.0 and 4.1 issues.
The spkm3 gss mechanism never caught on (hence also lipkey, which was based on it); by the time it was implemented, protocol shortcomings were found, and it was decided a new mechanism would need to be specified. See SPKM3 Issues.
Testing: A now-defunct NFSv4 testing project compiled a bunch of tests that might be worth running on NFSv4, with some results on early code, etc.:
- Testing tools
- Emulating tools
- Functional testing
- Robustness testing
- Tests needed
- Testing methodologies
- Test matrix
- Testing forecast roadmap