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Summary: 40
File System Implementation
In this note, 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 hard-
ware features to make some aspect of the file system work bet-
ter (though we will want to pay attention to device character-
istics to make sure the file system works well). Because of the
great flexibility we have in building a file system, many differ-
ent ones have been built, literally from AFS (the Andrew File
System) [H+88] to ZFS (Sun's Zettabyte File System) [B07]. All
of these file systems have different data structures and 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
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