This is what happens, children, when you think you are smarter than the array auto-tiering software and force all your LUNs onto specific disks. You end up with terrible balance and bad performance.
Quick Legend: This is a timelapse of 24 hours in the life of the array. The bottom rows (the small squares) are the individual disks, with the hot upper left section being all SATA drives, the rest are FC drives. Clearly a pretty strong imbalance. The larger squares above that are the actual CPUs that control the data flow.