What does shared file system mean?

By establishing the shared file system environment, sysplex users can access data throughout the file hierarchy from any system in the sysplex.

The best way to describe the benefit of this function is by comparing what was the file system sharing capability prior to the introduction of shared file system support with the capability that exists now. Consider a sysplex that consists of two systems, SY1 and SY2:

Users logged onto SY1 can write to the directories on SY1. For users on SY1 to make a change to file systems mounted on SY2's /u directory, they would have to log onto SY2.
The system programmer who makes configuration changes for the sysplex needs to change the entries in the /etc file systems for SY1 and SY2. To make the changes for both systems, the system programmer must log onto each system.

With shared file system support, all file systems that are mounted by a system participating in a shared file system are available to all participating systems. In other words, once a file system is mounted by a participating system, that file system is accessible by any other participating system. It is not possible to mount a file system so that it is restricted to just one of those systems. Consider a sysplex that consists of two systems, SY1 and SY2:

A user logged onto any system can make changes to file systems mounted on /u, and those changes are visible to all systems.
The system programmer who manages maintenance for the sysplex can change entries in both /etc file systems from either system.

The term participating group is used to identify those systems that belong to the same SYSBPX XCF sysplex group and have followed the required installation and migration activities to participate in a shared file system.

There is also greater availability of data in case of system outage, and a greater flexibility for data placement and the ability for a single BPXPRMxx member to define all the file systems in the sysplex.