Db2 for z/OS support for asynchronous CF duplexing

When the coupling facility (CF) is set up in duplex mode, Db2 for z/OS data sharing performance can improve if asynchronous CF duplexing is in effect.

With asynchronous CF duplexing, multi-site data sharing groups that implement duplexing all Db2 CF structures can have continuous availability without significant performance impact after site failures.

Asynchronous CF duplexing for the lock structure has the following prerequisites:

z/OS 2.2, with the PTF for APAR OA47796
Firmware support for Coupling Facility Control Code (CFCC) with service level 02.16
CF-to-CF connectivity through coupling links

If those prerequisites are met, you can enable asynchronous CF duplexing by setting the DUPLEX option in the coupling facility resource management (CFRM) policy to one of the following values:

DUPLEX(ENABLED,ASYNCONLY)
DUPLEX(ENABLED,ASYNC)
DUPLEX(ALLOWED,ASYNCONLY)
DUPLEX(ALLOWED,ASYNC)

See Options for duplexing for details.

Asynchronous duplexing and coexistence with Db2 11

When a data sharing group is in coexistence mode with Db2 11 members, asynchronous duplexing of the lock structure cannot be established. When a Db2 11 member joins a data sharing group, the connection to the lock structure is switched to either simplex mode or to synchronous duplexing mode, depending on the DUPLEX option in the CFRM policy for the lock structure. When asynchronous duplexing is no longer active, z/OS issues message IXC522I. The structure can switch back to asynchronous duplexing when there are no active Db2 11 members left in the group.

Switching from asynchronous CF duplexing

You can switch from asynchronous CF duplexing to a simplex lock structure or to synchronous duplexing of the lock structure at any time by changing the CFRM policy for the lock structure, and rebuilding the lock structure to activate the new policy.