UNIX Filesystems: Evolution, Design, and Implementation

Development of the SVR4 VFS/Vnode Architecture

The development of the File System Switch (FSS) architecture in SVR3, the Sun VFS/vnode architecture in SunOS, and then the merge between the two to produce SVR4, substantially changed the way that filesystems were accessed and implemented. During this period, the number of filesystem types increased dramatically, including the introduction of commercial filesystems such as VxFS that allowed UNIX to move toward the enterprise computing market.

SVR4 also introduced a number of other important concepts pertinent to filesystems, such as tying file system access with memory mapped files, the DNLC (Directory Name Lookup Cache), and a separation between the traditional buffer cache and the page cache, which also changed the way that I/O was performed.

This chapter follows the developments that led up to the implementation of SVR4, which is still the basis of Sun's Solaris operating system and also freely available under the auspices of Caldera's OpenUNIX.