Method 1—VSAM SHAREOPTIONS(2 3)

If you are starting only one DFSMShsm host in a z/OS image, the following share option strategy provides maximum protection against accidental, non-DFSMShsm concurrent updates:

Define the CDSs with VSAM SHAREOPTIONS(2 3).
Use the GRS RNL exclusion capability to avoid propagating the VSAM resource of SYSVSAM for the CDS components to other systems.

This share option can also be used with RLS when starting DFSMShsm in a multiple DFSMShsm host environment under a single z/OS® image.

Note: The GRS RNLDEF statements cannot be used with method 1 when using RLS.

Cross-region share option 2 allows only one processor at a time to open a data set for output. If that data set is in the SYSTEMS exclusion list, the open is limited to a single z/OS system. This combination sets a limit of one open per processor with the expectation that the one open will be DFSMShsm. As long as DFSMShsm is active in each z/OS ystem, then no jobs, including authorized jobs, can update the CDSs.

If you define the CDSs with VSAM SHAREOPTIONS(2 3) and start DFSMShsm on multiple host environments, exclude the SYSVSAM resource related to the CDS components from being passed around the GRS ring. Figure 1 shows the RNLDEF statements that exclude the SYSVSAM resource from being passed around the GRS ring.

Figure 1. GRS RNLDEF Statements for SHAREOPTIONS(2 3)

RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(MCDS index name)
RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(MCDS data name)
RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(BCDS index name)
RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(BCDS data name)
RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(OCDS index name)
RNLDEF RNL(EXCL) TYPE(GENERIC) QNAME(SYSVSAM) RNAME(OCDS data name)

Attention:

Reserve contentions can occur when a site does not use a global serialization product and that site processes DFSMShsm and applications concurrently with VSAM data sets on the same volume.
Specify DISP=SHR for read-only utilities (Example: DCOLLECT). Specify DISP=OLD (which allows an exclusive enqueue on the data set) for utilities that alter the CDSs (Example: AMS REPRO and IMPORT).
Do not attempt to reorganize your CDSs while DFSMShsm is running on any processor that uses those CDSs. See HSMPRESS for a sample job for reorganizing CDSs.
You can use this share option to access the CDSs in RLS mode. When you use RLS in a VSAM SHAREOPTIONS(2 3) mode, VSAM allows non-RLS access that is limited to read processing. Example: EXAMINE or REPRO access.