Basics of the z/OS UNIX file system
The z/OS UNIX file system, like other UNIX systems, is a hierarchical file system that consists of the
root file system and all the file systems that are added to it. Files are members of a directory,
and each directory is in turn a member of another directory at a higher level. The highest level of
the hierarchy is the root directory. Each instance of the system contains only one root directory.
Under the /usr/lpp directory are directories for z/OS elements and features; in this case, BookServer
and TCP/IP. For more information about hierarchical file systems, see z/OS UNIX System Services User's Guide.
A hierarchical file system consists of files, directories, and
additional file systems.
- The files contain data or programs. A file that contains a load module or shell script or REXX program is called an executable file. Files are kept in directories.
- The directories contain files, other directories, or both. Directories are arranged hierarchically, in a structure that resembles an upside-down tree, with the root directory at the top and the branches at the bottom. The root is the first directory for the file system at the top of the tree and is designated by a slash (/).
- The additional local or remote file systems are mounted on directories of the root file system or other file systems.
Some notes to consider:
- File systems must be cataloged in the master or user catalog in order for the file systems to be mounted by z/OS UNIX.
- File systems have multiple volume support. The support allows
a file system to span a total of 59 volumes with limits of 123 extents
per volume and 255 extents across all volumes. The maximum size of
a file that is stored in a file system is the following
- 2**31 pages (4K bytes/page) = 2**43 bytes
- If you are sharing file systems in a sysplex, you know that the term "root file system" is called the version file system. Think of the version file system when you see "root file system".