z/OS V1R6.0 DFSMS Access Method Services for Catalogs

DEFINE CLUSTERDEFINE RECORDS allocates sufficient space to the specified number ofrecords, but factors unknown at define time (such as key compression ormethod of loading records) can result in inefficient use of the space allocated.This might prevent every data CA from being completely used, and you mightbe unable to load the specified number of records without requiring secondaryallocation.When multiple volumes are used for a data set, these rules and conditionsapply:vvvvvThe first volume is defined as the prime volume. The initial allocation of adata set is on the prime volume. The remaining volumes are defined ascandidate volumes.A data set’s primary space allocation (defined for each data set) is theamount of space initially allocated on both the prime volume and on anycandidate volumes the data set extends to.A data set’s secondary space allocation (if it is defined) is the space allocatedwhen the primary space is filled and the data set needs additional space onthe same volume.If a data set extends to a candidate volume, the amount of space initiallyallocated on the candidate volume is the primary space allocation. If thedata set extends beyond the primary allocation on the candidate volume,then the amount of space allocated is the secondary space allocation.With a DEFINE request, the primary space allocation must be fulfilled infive DASD extents unless the Space Constraint Relief option is specified inthe associated SMS data class.However, the request is not successful if you do not fulfill each secondaryspace allocation in five DASD extents. A DASD extent is the allocation ofone available area of contiguous space on a volume. For example, if a dataset’s primary space allocation is 100 cylinders, you must allocate a maximumof five DASD extents that add up to 100 cylinders.Secondary amounts can be allocated on all volumes available to contain partsof the cluster regardless of the key ranges.You can specify the amount of space as a parameter of CLUSTER, as aparameter of DATA, or as a parameter of both. When a key-sequenced clusteris being defined, and the space is a parameter of:vvCLUSTER, the amount is divided between the data and index components.The division algorithm is a function of control interval size, record size,device type, and other data set attributes.If the division results in an allocation for the data component that is not anintegral multiple of the required control area size, the data component’sallocation is rounded up to the next higher control area multiple. Thisrounding can result in a larger total allocation for your cluster.DATA, the entire amount specified is allocated to the data component. Anadditional amount of space, depending on control interval size, record size,device type, and other data set attributes, is allocated to the indexcomponent.To determine the exact amount of space allocated to each component, list thecluster’s catalog entry, using the LISTCAT command.The primary and each secondary allocation must be able to be satisfied in fiveDASD extents; otherwise, your DEFINE or data set extension is unsuccessful.Chapter 14. DEFINE CLUSTER 149