An impressive amount of work has been done to date on improving the electrical efficiency of various data center components. The data storage industry has begun to see the fruits of this effort, with increased power supply and fan efficiencies. However, storage presents other significant opportunities for energy conservation, through various types of capacity optimization, that are not captured in electrical efficiency discussions. As data storage uses on the order of 25% of IT power in an average data center, these other opportunities bear examination. This article presents a survey of emerging storage technologies which positively impact energy usage and presents current thinking in the storage industry regarding their relative effectiveness. It also attempts to set a baseline for configurations against which improvements in capacity and energy use can be made.