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

DEFINE CLUSTERprimaryAllocates the initial amount of space to the cluster.secondaryAllocates an amount of space each time the cluster extends, as a secondaryextent. You can use this secondary allocation to add space for the data orindex components of the cluster. A VSAM data set can be expanded to 123extents per volume. If this is a multi-volume VSAM data set, then theVSAM component can be extended to a maximum of 255 extents combinedover all volumes.VOLUMES(volser[ volser...])Specifies the volumes on which a cluster’s components are to have space. Ifyou do not use the MODEL parameter, or if the cluster is not SMS-managed,VOLUMES must be used either as a parameter of CLUSTER, or as a parameterof both DATA and INDEX.VOLUMES can be specified or modeled for a data set that is to beSMS-managed; know that the volumes specified might not be used and resultin an error. See z/OS DFSMSdfp Storage Administration Reference for informationabout SMS volume selection.Volumes are always allocated in the order specified. If there is not enoughspace on the volume, the allocation is not successful. For non-SMS-manageddata sets, the primary space is allocated on the first volume in the list. Whenyou extend the data set because the first allocation is full, the volumes are usedin the order in which they appeared in the DEFINE command.Letting SMS select the volume from the storage group reduces the chances ofallocation errors caused by insufficient space. If the data set is SMS-managedwith guaranteed space, SMS places the primary quantity on all the volumeswith sufficient space for later extensions. If the SMS-managed data set does nothave guaranteed space or is a key range data set, primary space is allocatedonly on the first volume. For SMS-managed VSAM data sets, the primaryspace might be allocated on a different volume from the one you specified.You can let SMS choose the volumes for SMS-managed data sets by coding an* for the volser with the VOLUMES parameter. If both user-specified andSMS-specified volumes are requested, the user-specified volser must be inputfirst in the command syntax. The default is one volume.For SMS-managed and non-SMS-managed data sets, you can specify up to 59volume serial numbers. If the combined number of volumes for a cluster andits associated alternate indexes exceeds 59, unpredictable results can occur.If the data and index components are to reside on different device types, youmust specify VOLUMES as a parameter of both DATA and INDEX. If morethan one volume is listed with a single VOLUMES parameter, the volumesmust be of the same device type.For SMS-managed data sets, if you want the data and index components to beon separate volumes for non-guaranteed space storage class requests, code twodifferent dummy names in the VOLUME parameter for each component. Ifthere are not enough volumes in the storage group to satisfy this requirement,the allocation will fail.If a guaranteed space storage class is assigned to the data sets (cluster) andvolume serial numbers are used, space is allocated on all specified volumes ifthe following conditions are met:vAll defined volumes are in the same storage group.150 z/OS V1R6.0 DFSMS Access Method Services for Catalogs