When writing to z/OS MVS data sets, the z/OS NFS Server has to buffer the RPC WRITE data so the buffered data logically appears sequential before the z/OS NFS Server call DFSMSdfp to write the blocks of data. To handle the large data sets and the random write from the NFS Clients, you can convert or port the z/OS NFS Server to AMODE64 (or LP64) to give it access to 64-bit Address Space (16 exabytes) for the logical data buffering and other control blocks management.

For z/OS V2R1, the meaning of the bufhigh, logicalcache, and cachewindow attributes have been changed to support the larger address space of AMODE64. See Table 1 for more information on these attributes.