Lock data sets

Lock data sets are VSAM key-sequenced data sets that record the client host IP address and, for NFS V4, the client identification as well as the client host name. Following a server outage, the z/OS NFS server reads the new lock data sets during initialization to determine which clients can reclaim locks. The z/OS 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 shutdown, at resource cleanup timeout, and at the end of the grace period at server startup.

Note: The lock data sets must always be allocated, even if nonlm is specified in the site attributes.

To create the lock data sets, perform the following tasks:

Allocate two empty VSAM KSDS data sets, on separate DASD volumes to reduce the possibility that a single failure would result in the loss of both data sets. Allocate them with the following attributes:
- Starting with offset 0, the first eight bytes in the record are the prime key field.
- The maximum record length of the lock data set is 2000 bytes, and the average record length is 1700 bytes.
```
DEFINE CLUSTER (NAME(lock_data_set_name) -
            VOL(vsam_volume_name) -
            CYL(1 1) -
            INDEXED -
            REUSE -
            KEYS(8 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 lock data sets.
Specify these two data sets to the LDBASE DD statement and LDBASE2 DD statement in the MVSNFS procedure (see Figure 1).
The server switches data sets after resource cleanup has run.
Resource cleanup is done at Network File System shutdown, resource cleanup timeout, and at the end of the grace period at server startup.

Figure 1 shows how to specify the lock data set on the LDBASE DD statement and LDBASE2 DD statement on the MVSNFS procedure.

Figure 1. Specifying the lock data set in the MVSNFS procedure

//*     LDBASE AND LDBASE2 ARE
//*     THE LOCK 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).
//*
//LDBASE  DD   DISP=SHR,DSN=MVSNFS.LDBASE
//LDBASE2 DD   DISP=SHR,DSN=MVSNFS.LDBASE2