Multicluster control data sets are control data sets that, because they are very large in size, require more than one volume to store their contents.

As your DFSMShsm workload increases so does the activity that each of the control data sets must record. As control data sets grow, they can require more space than the physical DASD devices allow (for example, the capacity of a 3390-3 is 2.8 GB). If this occurs, control data sets can be split across multiple volumes to accommodate their larger size. Only the MCDS and BCDS can be more than one cluster.