Key to Fast Crash Recovery: Statelessness

Stateless protocol

This simple goal is realized in NFSv2 by designing what we refer to as a stateless protocol. The server, by design, does not keep track of anything about what is happening at each client. For example, the server does not know which clients are caching which blocks, or which files are currently open at each client, or the current file pointer position for a file, etc. Simply put, the server does not track anything about what clients are doing; rather, the protocol is designed to deliver in each protocol request all the information that is needed in order to complete the request. If it doesn’t now, this stateless approach will make more sense as we discuss the protocol in more detail below.

Stateful protocol

For an example of a stateful (not stateless) protocol, consider the open() system call. Given a pathname, open() returns a file descriptor (an integer). This descriptor is used on subsequent read() or write() requests to access various file blocks, as in this application code (note that proper error checking of the system calls is omitted for space reasons):