Petascale Data Storage Institute (Final Report)
Peter Honeyman · 2012
pNFS is an extension to NFSv4 that helps clients overcome NFS scalability and performance barriers. Like NFS, pNFS is a client/server protocol implemented with secure and reliable remote procedure calls. pNFS departs from conventional NFS by allowing clients to access storage directly and in parallel. This helps overcome server bottlenecks inherent to NAS access methods. Making pNFS available to petascale researchers required coordinated progress in several dimensions, a confluence of multiple processes that took nearly ten years. The protocol had to be specified and published by the IETF. Nascent implementations had to track changes in the draft specification, changes in the Linux kernel, and interoperate with one another. The process by which modifications are accepted into the Linux kernel by maintainers and developers (and ultimately by Linus Torvalds himself) itself required consensus and compromise. Finally, pNFS support needed to be provided by the major Linux distributors (Red Hat, SUSE, etc.) and storage vendors (Netapp, EMC, IBM, Microsoft, etc.) on both the engineering and product sides. The specification requirement was met in December 2008, when the IETF approved the NFSv4.1 specification, which incorporates pNFS and pNFS file layouts, as a Proposed Standard as well as the (separate) specifications of pNFS object and block layouts. Throughout the PDSI project, CITI was the key contributor to the Linux-based, open source implementation of NFSv4.1 and pNFS. Considerable effort was devoted to the process of refining the IETF specification, which underwent dozens of preliminary drafts, rebasing implementations to the latest Linux kernel, which itself changed quarterly, and to testing interoperability with other developers. At last, the Linux pNFS implementation was incorporated into the Linux mainline kernel, although this was achieved after the PDSI project ended.