Restrictions on mounting file systems

The restrictions on mounting file systems are:

The mount point must be a directory. If it is not an empty directory, files in that directory are not accessible while the file system is mounted. The BPXPRMxx parmlib statement NONEMPTYMOUNTPT can be used to control how the system mounts the file systems on the non-empty mount points. The NOWARN option specifies that the mount is to take place without any warning message when the mount point is a non-empty directory. The contents of that directory are hidden for the duration of the mount. The WARN option specifies that the mount is to take place with a warning message when the mount point is a non-empty directory. The contents of that directory are hidden for the duration of the mount. The DENY option specifies that mounting is not to take place when the mount point is a non-empty directory. During OMVS initialization, if the mount point is contained in an NFS file system, the NONEMPTYMOUNTPT setting is not honored.
Only one file system can be mounted at a directory (mount point) at any one time.
Systems participating in shared file system capability can mount file systems that will be shared in read/write mode.
The file systems in the same file hierarchy cannot have the same name even if they are mounted on different mount points. This remains true whether real names or alias names are specified on the FILESYSTEM operands in BPXPRMxx or on the MOUNT command. If two file systems have the same name, they cannot be mounted.
There is an upper limit to the number of HFS or zFS file systems that can be mounted at one time in your system. For planning purposes, about 1K of storage is consumed below the 16M line for each mounted file system. You can limit the amount of storage that is consumed. To limit the amount, use the timeout capabilities of automount so that file systems are unmounted when they are not being used. This storage below the line is used for the data set allocation. If storage is not available and another data set allocation is requested, the system may be placed in a nonrestartable wait state.
Alternatively, you can specify SWA(ABOVE) in the BPXPRMXX parmlib member to force the storage for data set allocation to be obtained above the 16M line. See the BPXPRMxx topic in z/OS MVS Initialization and Tuning Referencefor more details about the SWA parmlib statement.