Introduction to File System Implementation

In this chapter, we introduce a simple file system implementation, known as vsfs (the Very Simple File System). This file system is a simplified version of a typical UNIX file system and thus serves to introduce some of the basic on-disk structures, access methods, and various policies that you will find in many file systems today.

The file system is pure software. Unlike our development of CPU and memory virtualization, we will not be adding hardware features to make some aspect of the file system work better (though we will want to pay attention to device characteristics to make sure the file system works well). Because of the great flexibility we have in building a file system, many different ones have been built, literally from AFS (the Andrew File System)“Scale and Performance in a Distributed File System” by John H. Howard, Michael L. Kazar, Sherri G. Menees, David A. Nichols, M. Satyanarayanan, Robert N. Sidebotham, Michael J. West… ACM TOCS, Volume 6:1, February 1988. A classic distributed file system; we’ll be learning more about it later, don’t worry. to ZFS (Sun’s Zettabyte File System)“ZFS: The Last Word in File Systems” by Jeff Bonwick and Bill Moore. Available from: http://www.ostep.org/Citations/zfs_last.pdf. One of the most recent important file systems, full of features and awesomeness. We should have a chapter on it, and perhaps soon will.. All of these file systems have different data structures and do some things better or worse than their peers. Thus, the way we will be learning about file systems is through case studies: first, a simple file system (vsfs) in this chapter to introduce most concepts, and then a series of studies of real file systems to understand how they can differ in practice.