NFSv4 Proxy in User Space on a massive cluster architecture: issues and perspectives Compute architectures evolved from single machines to big SMP clusters. Further evolutions will see larger machines designed as massive "clusters of clusters". In this new architecture, using NFS exported file systems is an issue: the server won't be able to support the huge number of clients from the compute machine. Use of proxy servers is a classical way of leveraging and reducing load on the server. The implementation of several NFS proxy servers is a solution to serve correctly the clients from a "cluster of clusters". CEA/DIF did develop NFS-GANESHA (https://nfs-ganesha.sourceforge.net/), a NFSv4 server running in user space able of managing very big caches (up to millions of records). It has different back-end modules and one of them turns the product into a User Space NFSv4 proxy server. This WiP topic will present an architecture deployement with several NFSv4 proxy servers in User Space (via NFS-GANESHA). Discussion will be made on related issues that appears in this scope (mostly coherency issues among the servers) and on various solutions (including slight protocol additions to NFSv4) to manage these issues.