Minimizing Metadata Access Latency in Wide Area Networked File Systems

Traditional network file systems, like NFS, do not extend to wide-area due to low bandwidth, high network latency, and dynamism introduced in the WAN environment. Metadata access latency is a significant performance problem for Wide Area File Systems, since metadata requests constitute a large portion of all file system requests, are synchronous, and cannot be cached at clients. We present WireFS, a Wide Area File System, which enables delegation of metadata management to nodes at client sites (homes). The home of a file stores the most recent copy of the file, serializes all updates, and streams updates to the central file server. WireFS uses access history to migrate the home of a file to the client site which accesses the file most frequently. We formulate the home migration problem as an integer programming problem, and present two algorithms: a dynamic programming approach to find the optimal solution, and a greedy algorithm which is non-optimal but is faster than the optimal algorithm. We show through extensive simulations that even in the WAN setting, access latency over WireFS is comparable to NFS’s performance in the LAN setting; the migration overhead is also marginal after the initial delegation.