http://www-128.ibm.com/developerworks/opensource/library/os-freebsd/
The FreeBSD file system is also somewhat reminiscent of its BSD UNIX past: It comes under the Fast File System (FFS) and the UNIX File System (UFS) monikers. Users are more likely to interact with the FFS portion of the file system, which regulates file and directory access. The UFS system, version 2 of which was released in 2003, sets the file system limits and the basic data structures organizing raw disk access. UFS and FFS are also available on NetBSD and OpenBSD. The more well-known journaling file systems current on Linux, like Reiser File System (Reiser FS) and Journaling File System (JFS), are not available on FreeBSD, mostly for security reasons. UFS has the additional advantage of stability and (now) scalability because its behavior and performance rely on research dating back more than two decades.