Performance Analysis and Optimization of the Hurricane File System ...

CHAPTER 3. HFS ARCHITECTURE 15
3.1.2 Logical Layer
HFS user−level library GNU C library K42 library
HFS
logical layer
disk
interface
user−level application
physical layer
disk
interface
device driver
virtual file system
file system interface
disk
interface
disk disk disk
Figure 3.1: HFS layers.
file cache
manager
file
representative
kernel
The logical layer provides naming, authentication, and locking services. Naming services include path name
lookup and caching. This layer was not ported since the VFS layer and the name space server components
of K42 handle these services. Krieger states that, “We are less concerned about this layer, since it is not
heavily involved when reading and writing file data, and hence is not performance critical” [34, p. 82].
3.1.3 Physical Layer
The physical layer maintains the mapping of logical file blocks to physical disk blocks. It handles file
structuring, disk block placement, load balancing, locality management, and cylinder clustering. This layer
is our area of focus since it contains the performance critical meta-data caches and implements the core
functionality of the file system. It will be described in more detail in Section 3.3.2.
3.1.4 File System Interface
The file system interface is similar to the Unix/Linux/GNU virtual file system interface definition. As shown
in Table 3.1, it contains functions to obtain and change file attributes, open and close files, obtain directory
listings, and read and write from and to the file system. The speed and scalability of these function calls
determines the overall speed and scalability of the file system.