pNFS overview

pNFS is a heterogeneous metadata protocol. The NFS client and server perform control and file management operations and delegate the responsibility for I/O to a storage-specific driver. By separating control and data flows, pNFS allows data to transfer in parallel from many clients to many storage endpoints.Distributing I/O across the bisectional bandwidth of the storage network between clients and storage devices removes the single server bottleneck.Figure 1 depicts the architecture of pNFS, which adds a layout driver, an I/O driver, and a file layout retrieval interface to the standard NFSv4 architecture.The layout driver understands the file layout of the storage system. A layout consists of all information required to access any byte range of a file. The layout driver uses the layout to translate read and write requests from the pNFS client into I/O
requests understood by the storage devices. The I/O driver performs I/O—e.g., iSCSI [29], Portals [30], SunRPC [31]—to the storage nodes. A benefit of pNFS is its ability to match the performance of the underlying storage system’s native client while continuing to support all standard NFSv4 features. This support is ensured by introducing pNFS extensions into a “minor version,” an extension mechanism that is part of the NFSv4 standard. In addition, pNFS does not impose restrictions that might limit the underlying file
system’s ability to provide quality-enhancing features such as usage statistics or storage management interfaces.