Advanced Topics › Global Data Set Integrity Facility › PDSE Type Data Set Considerations › PDSE Resource Sharing

PDSE Resource Sharing

CA MII is fully compatible with PDSE resource sharing. CA MII does not modify, enhance, or restrict PDS/E processing in any way. PDSE sharing is limited to a single sysplex in a pure global GRS environment, and the same restrictions apply, even when you are running CA MII. In this regard, CA MII neither enhances nor restricts PDSE sharing.

However, customers have shared DASD across sysplex (GRSPLEX) boundaries for years using CA MII. You cannot assume that CA MII provides the same enhanced sharing capabilities with PDSEs.

While CA MII propagates ENQ and RESERVE requests outside sysplex boundaries, and thus allows sharing of DASD outside the sysplex boundaries, PDSE ENQ requests are a notable exception. Because the PDSE code issues its SYSZIGW0 and SYSZIGW1 ENQs with RNL=NO, CA MII does not process these ENQs, and thus does not propagate these requests outside the sysplex. However, CA MIM propagates RNL=NO type ENQs running in a monoplex with GRS=NONE and PDSESHARING(NORMAL), including SYSZIGW0 and SYSZIGW1.

When using PDSEs, there are two possible modes of sharing:

• PDSESHARING(NORMAL)
• PDSESHARING (EXTENDED)
• You specify the sharing mode in the IGDSMSxx member of SYS1.PARMLIB or in a data set in the logical PARMLIB. You can use the MVS "DISPLAY SMS,OPTIONS" command to determine how the PDSESHARING option has been set in your active SMS address space on a given system.

PDSESHARING(NORMAL)

When sharing PDSEs in NORMAL mode, the PDSE can be shared by all systems for input only. This is the default mode setting. Only one writer is allowed per complex. Subsequent concurrent openers for output are terminated with a S213-70 ABEND.

When you specify PDSESHARING(NORMAL), the SYSZIGW0 and SYSZIGW1 ENQs are used in order to maintain PDSE integrity, and XCF services are not used. However, the PDSE code issues its SYSZIGW0 and SYSZIGW1 ENQs with RNL=NO specified. This precludes CA MII from managing these ENQs when they are issued on a system that is a member of a sysplex. This can cause integrity exposures in some environments.

PDSESHARING(EXTENDED)

When you specify PDSESHARING(EXTENDED), a PDSE can be shared for input and output in a single sysplex.

In EXTENDED mode, XCF services are used to pass information between systems in a single sysplex to maintain read and write integrity. Therefore, the sharing of PDSEs in EXTENDED mode requires a sysplex and is limited to the systems in the sysplex by definition.

With PDSESHARING(EXTENDED), the sharing of PDSEs is limited by XCF connectivity, not by the scope of the SYSZIGW0/1 ENQs. Therefore, the sysplex restriction in this case is due to the IBM PDSE architecture, not by the global serialization product (for example, CA MII).