pNFS

pNFS, or parallel NFS, is an extension to the Network File System (NFS) designed to improve scalable data access by allowing clients to read and write data stored on multiple storage targets in parallel. It was introduced with NFS version 4.1 and defined within the NFSv4.1 specification by the IETF. The core idea is to separate data I/O from metadata operations, enabling direct data paths to storage servers and enabling parallel I/O across several targets.

In operation, a client interacts with an NFSv4.1 server to obtain a layout, which is a directive that describes how a file’s data is distributed across storage devices and servers. With an active layout, the client can perform data I/O directly against the designated storage targets, potentially in parallel, while the metadata server remains responsible for metadata operations, consistency, and coordination.

pNFS defines several layout types. File layout describes data stored as regular files on storage servers. Block layout treats data as raw blocks on block storage devices. Object layout uses object storage backends. These layout types support different deployment models, such as distributing a file’s data across multiple data servers or backing storage with object storage services.

Benefits of pNFS include higher aggregate throughput, reduced load on the metadata server, and improved scalability for large, multi-target storage environments. Limitations include the need for compatible hardware and software, added administrative complexity, and varying performance gains depending on workload and deployment.

pNFS remains an optional extension of NFSv4.1 and is supported by various Linux and other NFS implementations, as well as some commercial NAS and storage products.