UNIX Filesystems: Evolution, Design, and Implementation

Digital UNIX / True64 UNIX

Digital UNIX, formerly called DEC OSF/1, is a microkernel-based implementation of UNIX utilizing the Mach microkernel and the BSD 4.3/4.4 versions of UNIX. For further details on microkernel-based UNIX implementations, see the section Microkernel Support for UNIX Filesystems, later in this chapter. With the merger between Compaq and Digital, the name of the operating system was changed to True64 UNIX. True64 now contains a considerable rewrite of many of the components of the OSF/1 kernel and differs substantially from the UNIX emulation on Mach, described in the section The Mach Microkernel later in this chapter.

From a filesystem perspective, True64 UNIX supports a large number of filesystems including UFS, NFS, procfs, and AdvFS (Advanced File System), a transaction-based filesystem that provides many features.

The True64 UNIX filesystem architecture was derived from the 4.3BSD Reno release but has, over the last several years, been modified to include a number of new features.

Steven Hancock's book True64 UNIX File System Administration Guide [HANC01] is an excellent source of information on the True64 filesystem architecture and individual filesystem implementations. The following sections provide a brief highlight of the main features.

Like most other versions of UNIX, True64 employs the same structures related to file access, namely file descriptors pointing to the system-wide file table whose entries point to vnodes.

The per-process file table ...