A method begins by a processing module storing a plurality of encoded data slices in a plurality of memory devices of a dispersed storage (DS) unit of a dispersed storage network (DSN) memory using a quantity load balancing function to substantially balance a quantity of encoded data slices stored within each of the plurality of memory devices, wherein data size of at least some of the plurality of encoded data slices is different. The method continues with the processing module determining whether an available memory imbalance exists between a first memory device of the plurality of memory devices and a second memory device of the plurality of memory devices. The method continues with the processing module migrating one or more encoded data slices between the first and second memory devices to reduce the available memory imbalance when the available memory imbalance exists.