NFSv4 doesn't have uids. It uses Kerberos principal names directly for authorization purposes, for example in the acls. It has referrals, so you can build a global namespace. If you build your own global name space, it's not global, is it? NFSv4 does not have what I would call a global name space. Afs does, unless you do something stupid like use non-qualified names like /afs/cs/.