Towards Dynamic Scripted pNFS Layouts

Today's network file systems consist of a variety of complex subprotocols and backend storage classes. The data is typically spread over multiple data servers to achieve higher levels of performance and reliability. A metadata server is responsible for creating the mapping of a file to these data servers. It is hard to map application specific access patterns to storage system specific features, which can result in a degraded IO performance. We present an NFSv4.1/pNFS protocol extension that integrates the client's ability to provide hints and I/O advices to metadata servers. We define multiple storage classes and allow the client to choose which type of storage fits best for its desired access pattern. Furthermore, we propose flexible, script based file layouts that describe a logical file's mapping to its storage locations by an interpreted script instead of a fixed mapping. We discuss the possibilities of such an extension, show that it integrates well with the pNFS protocol and show that the latency and compute overhead of interpreted layouts justifies the gained features.