A system and method is disclosed for performing maintenance on a mission critical system while minimizing unavailability of the system to users. The system includes software storage having at least production and maintenance portions. Initially, the maintenance and production portions are set to be identical and the system is programmed to operate from the production portion. During maintenance operations, the system is taken off line and the maintenance is performed only on the maintenance portion, leaving the production portion unaltered. Until the maintenance is complete, if the system is required to be available, it may be brought back on-line and directed to continue to operate from the production portion. Once maintenance is complete, the maintenance portion is designated as the production portion and vice versa. The system is then directed to operate from the newly maintained production portion.