Moving file systems to a back-level system

If you move a file system to a back-level system, existing NFS client connections to the files in that file system might be broken if Share Reservations are used. With Share Reservations, remote NFS clients can open files on z/OS® in such a way that no one else can open that file until the first program finishes and closes the file. For more information about Share Reservations, see the BPX1VOP callable service in z/OS UNIX System Services File System Interface Reference.

Share Reservations that attempt to deny reading or writing for files in a read-only file system are accepted but will not be enforced.

File systems cannot be remounted from read/write to read-only or from read-only to read/write while there are Share Reservations established on any file in that file system.

Restrictions: A file system cannot be moved to a back-level system while there are active Share Reservations on any file in the file system. You will have to move the file system to a sysplex member at the z/OS V1R7 release level or later. Alternatively, you can stop the applications at the NFS clients who have put reservations on the files, or wait for them to finish.

If an NFS client is going to open a file that has Share Reservations set:

That file must be owned by a system at the z/OS V1R7 level or higher before it can be opened.
If the file is owned by a remote system that supports Share Reservations, they are enforced at the owner for all opens within the sysplex.
If the file is owned by a remote system at a lower level, the client's open will fail. The reason code of the failure will indicate that the file system has to be moved to a sysplex member that is at the z/OS V1R7 release or later.

If the system goes down and there are Share Reservations on a file owned by a remote system:

If the file system is taken over by another z/OS V1R7 or later system, the reservations are reestablished at the new owner and enforced there.
If the file system is taken over by an owner that does not support Share Reservations, the NFS client's open is invalidated and subsequent operations from that client for this open are rejected. If you move the file system to a sysplex member that supports Share Reservations, the file can be reopened as it was before. You can use the AUTOMOVE parameter of the MOUNT command to restrict these takeovers to the systems that do support Share Reservations.