CS262A Reading Summary 8

A Fast File System for UNIX

M. McKusick et al
Summary by Feng Zhou
9/22/2002

1. Physical characteristics like rotational latency, seek time, as well as usage patterns are considered in the FFS file system organization. These are not considered in the original UNIX FS design. All the performance enhancement are done without changing the user interface.
2. Cylinder group and rotational positions are among the key techniques presented. The former, along with local allocation policies, improves performance by raising data locality. The latter shortens the rotational latency.
3. Important functional enhancements are done by changing internal data structures and adding system calls, with backward compatiblity. The addition of symbolic links, which I consider the most important one among them, makes the FS a lot more flexible.

One major flaw:

Regarding advisory file locks, "Almost no deadlock detection is attempted." No means of timeout or custom deadlock detector are discussed. What's more, the locking interface is blocking. So user applications will have neither ways to tell whether deadlocks has happened nor ways to get out of them.