The mount handle data sets are used to record active mounts during server operation and allow clients to stay mounted when the server is shut down and restarted. The Network File System alternates between two data sets to record this information; only one data set is used at a time, and it is switched at either shutdown or at resource cleanup timeout.

To create the mount handle data sets, perform the following tasks:

1. Allocate two empty VSAM KSDS data sets with the following attributes:
   • Starting with offset 0, the first 16 bytes in the record are the prime key field.
   • The maximum record length of the mount handle data set is 2000 bytes, and the average record length is 1700 bytes.

     DEFINE CLUSTER (NAME(mount_handle_data_set_name) -
                 VOL(vsam_volume_name) -
                 CYL(1 1) -
                 INDEXED -
                 REUSE -
                 KEYS(16 0) -
                 SHAREOPTIONS(1 3) -
                 RECSZ(1700 2000))    

     See GFSAMHDJ sample code for creating NFS mount handle data sets and lock data sets for sample JCL showing how to create the mount handle data sets.

2. Specify these two data sets to the FHDBASE DD statement and FHDBASE2 DD statement in the MVSNFS procedure (see Figure 1).
3. The server switches data sets after resource cleanup has run.
4. Resource cleanup is done at Network File System shutdown and resource cleanup timeout.

Figure 1 shows how to specify the mount handle data set on the FHDBASE DD statement and FHDBASE2 DD statement on the MVSNFS procedure.

//*     FHDBASE AND FHDBASE2 ARE
//*     THE MOUNT HANDLE DATA SETS.
//*     THEY NEED TO BE PREALLOCATED
//*     AS EMPTY VSAM KSDS DATA SETS.
//*     THEY WILL BE USED ALTERNATELY.
//*     SAMPLE JCL CAN BE FOUND IN HLQ.NFSSAMP(GFSAMHDJ).
//*
//FHDBASE  DD   DISP=SHR,DSN=MVSNFS.FHDBASE
//FHDBASE2 DD   DISP=SHR,DSN=MVSNFS.FHDBASE2