A request to alter a duplexed structure is handled serially, with the old structure completing the alter process before the alter of the new structure is started. The same set of parameters for the alter is applied to each instance of the structure. However, conditions in the coupling facility, such as the coupling facilities might be of different CFLEVELs or might not have the same amount of available free storage, might not allow both alter operations to complete with the same results. For example, if both instances of the structure are altered to different sizes, it is the responsibility of the connector to manage the difference — in this case, to issue another alter request to resize the larger structure to the size of the smaller structure. Completion of the second duplexing alter request would take less time than the first duplexing alter request because the smaller instance of the structure would already be at the requested size.