With concerns about power consumption and energy costs growing, efforts are underway to make data centers more "green" (energy efficient) and sustainable (reducing the use of non-renewable resources). In most data centers, servers draw more energy than storage devices; still, it has been estimated that all of the disk drives spinning around the world today generate emissions equivalent to 9 million cars annually. Some analysts suggest that in 2008 half of all data centers won't have the power they need - and yet, many data centers waste as much as 60% of their energy on inefficient server and storage infrastructures. To encourage power reductions some utility companies and state energy auditors are offering rebate programs; consultants have developed new services to analyze power profiles and suggest improvement strategies.