File Virtualization with DirectNFS

There is a definite trend in the Enterprise Storage industry to move from Network Attached Storage (NAS) solutions to high performance Storage Area Networks (SAN). This transition is not easy because of the well-entrenched NAS infrastructure that has already been deployed. This paper attempts to define a file system that can leverage the existing NAS software infrastructure along with evolving SAN technology to provide the benefits of High Performance storage access while reducing the cost of migrating to these networks. In this paper, we propose a new network file system, DirectNFS, which allows NAS clients to take full advantage of the performance and scalability benefits of SANs. In order to achieve this goal, the system presents a NAS interface to existing NAS clients while allowing DirectNFS clients to access storage directly over shared SAN, i.e. clients bypass the server for data access. A server maintains the NAS interface for legacy clients and arbitrates access to metadata by DirectNFS (SAN aware) clients. This metadata server ensures that the system is operable for both legacy NAS clients as well as DirectNFS clients. The communication protocol of DirectNFS is designed as an extension of traditional network file systems protocols, such as NFS and CIFS. A prototype of DirectNFS has been built for Linux, as an extension to the native NFSv2 implementation. Initial results demonstrate that the performance of data intensive operations such as read and write is comparable to that of local file systems, such as ext2.