A managing unit included in a distributed storage network (DSN) determines resource availability information. The resource availability information includes information indicating a number of memory devices available to be used for storage of encoded data slices. The management unit then chooses dispersal parameters based on the resource availability information. The dispersal parameters are chosen to satisfy a performance threshold associated with storage of the encoded data slices in the DSN, but subject to a constraint requiring a pillar width associated with the encoded data slices to be no larger than the number of memory devices available. The management unit creates a number of storage units, wherein the number of storage units is constrained to be greater than the pillar width, and wherein one or more of the number of memory devices is assigned to each of the number of storage units. The management unit then instantiates a DSN memory that includes the number of storage units.