Radical energy savings method 5: Use SSDs for highly active read-only data sets
SSDs have been popular in netbooks, tablets, and laptops due to their speedy access times, low power consumption, and very low heat emissions. They're used in servers, too, but until recently their costs and reliability have been a barrier to adoption. Fortunately, SSDs have dropped in price considerably in the last two years, making them candidates for quick energy savings in the data center -- provided you use them for the right application. When employed correctly, SSDs can knock a fair chunk off the price of powering and cooling disk arrays, with 50 percent lower electrical consumption and near-zero heat output.
One problem SSDs haven't licked is the limited number of write operations, currently around 5 million writes for the single-level-cell (SLC) devices appropriate for server storage. Lower-cost consumer-grade multilevel-cell (MLC) components have higher capacities but one-tenth of SLCs' endurance.
The good news about SSDs is that you can buy plug-compatible drives that readily replace your existing power-hungry, heat-spewing spinners. For a quick power reduction, replace large primarily read-only data sets, such as streaming video archives, with SSD. You won't encounter SSD wear-out problems, and you'll gain an instant performance boost in addition to reduced power and cooling costs.
Go for drives specifically designed for server, rather than desktop, use. Such drives typically have multichannel architectures to increase throughput. The most common interface is SATA 2.0, with 3Gbps transfer speeds. Higher-end SAS devices, such as the Hitachi/Intel Ultrastar SSD line, can achieve 6Gbps speeds, with capacities up to 400GB. Although SSD devices have encountered some design flaws, these have been primarily with desktop and laptop drivers involving BIOS passwords and encryption, factors not involved in servers' storage devices.
Do plan to spend some brain cycles monitoring usage on your SSDs, at least initially. Intel and other SSD makers provide analysis tools that track read and write cycles, as well as write failure events. SSD disks automatically remap writes to even out wear across a device, a process called load leveling, which can also detect and recover from some errors. When actual significant write failures begin occurring, it's time to replace the drive.
Radical energy savings method 6: Use direct current in the data center
Yes, direct current is back. This seemingly fickle energy source enjoys periodic resurgences as electrical technologies ebb and flow. The lure is a simple one: Servers use direct current internally, so feeding that power to them directly should reap savings by eliminating the AC-to-DC conversion performed by a server's internal power supply.
Direct current was popular in the early 2000s because the power supplies in servers of that era had data center conversion efficiencies as low as 75 percent. But then power supply efficiencies improved, and data centers shifted to also-more-efficient 208-volt AC. By 2007, direct current fell out of favor. InfoWorld even counted it among the myths in our 2008 article "10 power-saving myths debunked." Then in 2009 direct current bounced back, owing to the introduction of high-voltage data center products.
In the earliest data centers, utility-supplied 16,000 VAC (volts of alternating current) electricity was first converted to 440 VAC for routing within a building, then to 220 VAC, and finally to the 110 VAC used by the era's servers. Each conversion wasted power by dint of being less than 100 percent efficient, with the lost power being cast off as heat (which had to be removed by cooling, incurring yet more power expense). The switch to 208 VAC eliminated one conversion, and with in-server power supplies running at 95 percent efficiency, there wasn't any longer much to gain.
But 2009 brought a new line of data center equipment that could convert 13,000 VAC utility power directly to 575 VDC (volts of direct current), which can then be distributed directly to racks, where a final step-down converter takes it to 48 VDC for consumption by servers in the rack. Each conversion is about twice as efficient as older AC transformer technology and emits far less heat. Although vendors claim as much a 50 percent savings when electrical and cooling reductions are combined, most experts say that 25 percent is a more credible number.
This radical approach does require some expenditure on new technology, but the technologies involved are not complex and have been demonstrated to be reliable. One potential hidden cost is the heavier copper cabling required for 48 VDC distribution. As Joule's Law dictates, lower voltages require heavier conductors to carry the same power as higher voltages, due to higher amperage. Another cost factor with data centers is the higher voltage drop incurred over distance (about 20 percent per 100 feet), compared to AC. This is why the 48 VAC conversion is done in the rack rather than back at the utility power closet.
Of course, converting to direct current requires that your servers can accommodate 48 VDC power supplies. For some, converting to DC is a simple power supply swap. Chassis-based servers, such as blade servers, may be cheaper to convert because many servers share a single power supply. Google used the low-tech expedient of replacing server power supplies with 12V batteries, claiming 99 percent efficiency over a traditional AC-powered UPS (uninterruptible power supply) infrastructure.
If you're planning a server upgrade, you might want to consider larger systems that can be powered directly from 575 VDC, such as IBM's Power 750, which recently demolished human competitors as Watson on the "Jeopardy" game show. Brand-new construction enjoys the advantage of starting with a clean sheet of paper, as Syracuse University did when building out a data center last year, powering IBM Z and Power mainframes with 575 VDC.