You can even mount a different ROOT file system without an IPL, if necessary.
The SETOMVS RESET command allows you to add FILESYSTYPE, NETWORK, and SUBFILESYSTYPE statements to BPXPRMxx without an IPL.
If you have syntax errors in your BPXPRMxx member, you will be prompted for another BPXPRMxx member during OMVS initialization. If you respond with ENTER - a null reply, you will get the minimal OMVS environment and you may need to IPL to bring up your OMVS environment. It would be a good idea to keep a known good parmlib member available to avoid this situation. IBM provides a sample BPXPRMXX in SYS1.SAMPLIB.
OMVS now supports temporary file systems (TFS), which are in-storage temporary filesystems. In fact, in the minimal OMVS environment, your ROOT file system is a TFS. You can also MOUNT a TFS. Since it is in-storage, a TFS provides high performance I/O. When you UNMOUNT a TFS or bring down the system, all the data in the TFS goes away.
Information on BPXPRMxx and the SETOMVS command can be found in the following publications:
You can display the current limits for OMVS and current/high-water usage levels for various global resources using the command D OMVS,L. You can display the limits which apply to individual processes using the command D OMVS,L,PID=nnnn where nnnn is the process id; again, current usage and high-water consumption are also reported.
z/OS, OMVS and Open MVS are trademarks of IBM Corporation.