The z/OS NFS server handles data set serialization and sharing differently, depending on the type of data set:

Physical sequential

The server ensures physical sequential data set read/write integrity by SVC 99 dynamic allocation with exclusive option whenever a physical sequential data set is opened for output. Otherwise, it allocates with share option.

Virtual storage access method (VSAM)

The server dynamically allocates a VSAM data set with share option and allows the VSAM access method to manage data sharing using the shareoptions specified during data set definition.

Partitioned data set extended (PDSE)

The server dynamically allocates a PDSE data set with share option and allows the PDSE functions to manage the serialization of the PDSE data set and its members.

Partitioned data set (PDS)

For read and write, the z/OS NFS server issues ENQ SHR on QNAME=SYSDSN and RNAME=data_set_name (through an SVC 99). For write, the server issues an exclusive ENQ against QNAME=SPFEDIT and RNAME=data_set_name.member_name, in addition to the serialization of resources by SVC 99. For all MVS™ users who are allocating their data set with exclusive status, this provides write protection. It only provides read integrity for ISPF users.