1. A method for use in a dispersed storage system, the method comprising: generating a set of encoded data slices from a data segment of data in accordance with dispersed storage error encoding parameters, wherein the set of encoded data slices includes X error coded (EC) slices per data segment and where X represents a width of an error encoding function; determining a security parameter and one or more of environmental and performance variables for storing the set of encoded data slices, wherein the security parameter indicates a desired level of security associated with a particular operating system in one or more storage units within the dispersed storage system and the one or more of environmental and performance variables includes at least one of a storage system's environment at a geographic location, construction, cost, operating performance, retrieval time, level of security, portability, power considerations, or availability; identifying a plurality of sets of the storage units of the dispersed storage system based on the one or more of environmental and performance variables; and selecting, from the plurality of sets of storage units, storage units to form a set of storage units for storing the set of encoded data slices based on the security parameter.