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.