true redundancy would mean you have twice the UPS you need so that if UPS1 fails UPS2 can take the entire load. UPS redundancy is viewed in terms of modules that can support the load in a distributed manner such that if n modules can service the load you would install (n+1) or (n+2) modules so that if a single module were to fail, the technician would come in with a new module and hot swap it with the failed module so the load is protected at all times with at least n modules.