For a data set to be opened for VSAM RLS processing, VSAM RLS processing must be available, and the LOG parameter must be specified on the DEFINE CLUSTER or the ALTER CLUSTER command for the data set. Additionally, if the data set is currently assigned to a CF cache structure, that cache structure must be available. If the data set is not currently assigned to a CF cache structure, a cache set must be specified on the storage class, and at least one of the associated CF cache structures must be available.