Which is higher availability 2N or N+2?

Modular scalable solutions continue to drive our industry to improved efficiency and availability. Most know about modular cabling infrastructure, CRAC units with VFDs and scalable UPS technology, but did you know you could also have modularity and scalability with your chillers?

Most understand that modular solutions improve efficiency, but many believe that a 2N design is higher availability than a N+2 design. Not so fast, 2N is 2 component failures away from an outage where N+2 in a modular design is typically 3 components away from having reduced capacity. So why doesn't Uptime consider N+x designs for any of the critical components in it's tiering ratings? For that matter why isn't there a data center rating system that considers the improved availability of N+x designs?