This section tells you how to define the CICS® availability manager (CAVM) data sets. The CAVM is the mechanism that enables active and alternate CICS regions to coordinate their processing when XRF=YES is coded as a system initialization parameter. If you code XRF=NO, these data sets are not used. The CAVM requires two data sets: the XRF control data set and the XRF message data set.
This pair of data sets is logically a single entity that contains:
Both the active and alternate CICS regions must refer to the same pair of data sets. You define these data sets, but must not try to initialize them, and you are recommended to place the data sets on separate volumes. The first time they are used, CICS recognizes them as a new pair of data sets. If they are new, CICS initializes them in such a way that, from then on, they can be used only as a pair with the original generic APPLID and for their original purpose (that is, as either an XRF message data set or an XRF control data set). If you need to redefine either data set, for any reason, you must redefine both of them.
You must define a separate pair of data sets for each generic APPLID in use. If a CICS complex consists of, for example, five regions, five pairs of data sets must be defined.
You do not need to take backup copies of these data sets because when neither of the active or alternate CICS regions is running, you can always start with a fresh pair of data sets.
Why have two data sets? Because of RESERVE commands issued by other MVS™ images in a multi-MVS environment, a shared DASD volume may become inaccessible for periods ranging from milliseconds to perhaps a minute. By making use of two data sets, placed on different volumes, CAVM can greatly reduce the risk that, by preventing surveillance signals from being written, normal RESERVE activity might cause the unnecessary takeover of a CICS region that was running normally.
If the access paths to the two volumes are separate, CAVM is also less vulnerable to hardware failures.
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