Recently I ran into an environment with a couple of VNX5700 systems that were attached to the front-end SAN switches with only two ports per storage processor. The customer was complaining: performance was OK most of the time but at some times during the day the performance was noticeably lower. Analysis revealed that the back-end was coping well with the workload (30-50% load on the disks and storage processors). The front-end ports were a bit (over)loaded and spewing QFULL errors. Time to cable in some extra ports and to rebalance the existing hosts over the new storage paths!
