When setting up a shared file system in a sysplex, do not assume that with shared file systems, two systems can share a common file system for /etc, /tmp, /var, and /dev. This is not the case. Even with shared file systems, each system must have specific file systems for each of these mount points. The file systems are then mounted under the system-specific file system (see Figure 3). With shared file system support, one system can access system-specific file systems on another system. (The existing security model remains the same.) For example, while logged onto SY2, you can gain read/write access to SY1's /tmp by specifying /SY1/tmp/.

Be aware that when SYSPLEX(YES) is specified, each FILESYSTYPE in use within the participating group must be defined for all systems participating in a shared file system. The easiest way to accomplish this is to create a single BPXPRMxx member that contains file system information for each system participating in a shared file system. If you decide to define a BPXPRMxx member for each system, the FILESYSTYPE statements must be identical on each system. To see the differences between having one BPXPRMxx member for all participating systems and having one member for each participating system, see the two examples in Scenario 2: Multiple systems in the sysplex using the same release level.

In addition, facilities required for a particular file system must be initiated on all systems in the participating group. For example, NFS requires TCP/IP; if you specify a FILESYSTYPE of NFS, you must also initialize TCP/IP when you initialize NFS, even if there is no network connection.

Tip: When using the TSO/E MOUNT command to set up system-specific file systems, specify the UNMOUNT parameter. Then, if data sets are replaced during a reIPL, the new data sets are mounted as the original file systems.