In datacenter storage, green is not about what you buy but how you use it The real or imagined concern of IT shops to make datacenters greener, both to save the environment and to reduce energy costs within IT, has given the marketing campaigns of server hardware vendors a whole new dimension. Storage vendors didn’t miss many beats before joining the chorus. Small-form-factor hard drives (i.e., laptop-size, 2.5-inch drives) are already showing up in enterprise servers and storage arrays because they can save power over the bigger 3.5-inch drives. In addition, as SSDs (solid-state drives) become less expensive, we can expect they too will be used in enterprise storage systems for their lower power usage as well as their higher performance. How much should IT care about these developments? Frankly, there is lots of room for debate when discussing greener storage. If SSDs failed to extend the battery life of the MacBook Air and other laptops, why should we believe they will reduce power consumption in the datacenter? And while it’s clear that small-form-factor drives are significantly more energy efficient than 3.5-inch disk drives, some of the real savings is lost due to the lower capacity of 2.5-inch drives. On the plus side, in InfoWorld’s tests, a 12-drive Infortrend array based on 2.5-inch disks performed on par with similar arrays based on 3.5-inch drives, while consuming about 60 percent of the power (see review). A more promising direction, at least under the right circumstances, is indicated by new storage systems that have the ability to spin drives down or reduce the rotational speeds of drives when demand is low. In operations that are 8×5 rather than 24×7, these capabilities could save large amounts of energy, both in the power consumed by the storage systems in the first place as well as by the cooling required to keep the systems happy. How much is really to be saved with these technologies remains to be seen. Take the experience of laptops with SSDs, for instance. The reason battery life with SSDs didn’t improve over that with standard hard drives is partly because the laptops automatically spin the drives down when they’re not in use. It’s also because substantial gains have been made in the energy efficiency of regular hard drives. You already know that replacing an existing array of drives with a new array supporting drives that spin down is not going to save you any money. The relatively small cost savings on power and cooling is not going to pay for an entire new storage system and drives. In fact, even when you’re buying new storage on a standard replacement schedule, depending on what you pay for power, it may be difficult to justify anything more than a very small premium over standard storage to get the spin-down capability. Given the much greater savings to be realized by more efficient power supplies and processors in servers, there are other places that a green budget can be spent to better effect. Even so, if the circumstances are correct — namely, in an 8×5 operation — the ability to spin drives down for as many as 15 hours a day could save 5 to 15 watts per drive. Taking 10 watts as average, an array with 16 drives would use 160 watts, or about as much as a lightbulb. If you’d turn the lights off in the server room when you leave, why not spin the drives down when no one’s using them?