Ensuring Continuous Availability of Couple Data Sets

When an alternate CDS exists for a given CDS type and the current primary CDS fails, XCF makes this alternate the primary CDS. After this switch, however, an alternate CDS no longer exists, and if the current primary CDS also fails, the problems that were to be avoided by the creation of an alternate occur again. To avoid this single-point-of-failure situation, SA z/OS provides a recovery mechanism that tries to ensure that an alternate CDS is always available for every CDS type used.

SA z/OS creates a new alternate CDS in the following two situations:

• During initialization, SA z/OS checks that an alternate CDS is specified for every primary CDS. If there is a primary CDS for which no alternate CDS exists, SA z/OS automatically creates it.
• At runtime, SA z/OS ensures that a new alternate is created whenever the current alternate has been removed or switched to the primary one.