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Improving the Write Performance of an NFS Server

Chet Juszczak
Digital Equipment Corporation


The Network File System (NFS) utilizes a stateless protocol between clients and servers; the major advantage of this statelessness is that NFS crash recovery is very easy. However, the protocol requires that data modification operations such as write be fully committed to stable storage before replying to the client. The cost of this is significant in terms of response latency and server CPU and I/O loading. This paper describes a write gathering technique that exploits the fact that there are often several write requests for the same file presented to the server at about the same time. With this technique the data portions of these writes are combined and a single metadata update is done that applies to them all. No replies are sent to the client until after this metadata update has been fully committed, thus the NFS crash recovery design is not violated. This technique can be used in most NFS server implementations and requires no client modifications.

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