Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
http://xenserver.org/blog.html?view=entry&id=98
One of the biggest changes is moving to CentOS 7 in the Dom0.
NFSv4 is only for security, typically you want to avoid this in a production virtualization environment. You would want to be on NFSv3 for performance reasons.