Greener Datacentres


There is a crisis because the cost of providing energy is rising and some datacentre hotspots risk being unable to get enough power to run the datacentres. For every watt of electricity used to power servers, datacentres are typically consuming two to three watts on cooling. Worldwide, the cost of electricity is going up, and while some businesses may have the option to relocate their datacentres to areas where there is a cheap and abundant electricity supply, many more will not have that option.

Solving storage power and cooling concerns

Many total cost of ownership (TCO) models are seriously outdated and wildly inaccurate because they haven’t been updated to include the increased cost to power and cool storage arrays, storage area network (SAN) switches and hosts. “Through 2009, energy costs will emerge as the second-highest operating cost in 70% of worldwide datacentre facilities,” declares Michael Bell, research vice president at Gartner, in a recent report. In addition, analysts expect U.S. companies will spend twice as much on power and cooling by 2009 as they did to acquire their IT devices. Today, servers account for 40% of the datacentre’s overall power consumption. Storage isn’t far behind, taking 37% of the overall power.

Power costs aren’t the only factor forcing organisations to rethink their TCO analyses. The cost of end-of-life disposal and emerging green regulations that require cradle-to-grave energy tracking — costs that IT managers previously paid scant attention to — also threaten to become significant factors. Even real estate prices are a factor as IT managers wrestle with packing equipment more densely into costly floor space or spreading it out to facilitate more efficient air flow and cooling.

While storage prices on a cost-per-gigabyte basis continue to drop, storage managers will find their best budgeting efforts undermined by power, disposal, energy tracking and real estate costs. However, the problem isn’t insurmountable. Vendors are ramping up energy-efficient green systems and tools to manage energy usage. By 2011, Gartner expects power demands to level off or even decline as innovations and best practices combine to contain the problem. In the meantime, IT managers still have to deal with the problem.

Unsustainable cost increases

The ugly secret of smaller, faster, cheaper is that just because we can make it smaller and buy more of it, doesn’t mean it is any more energy efficient. To the contrary, smaller and cheaper means companies are buying more devices and packing them more densely into the datacentre. Even if the individual devices use less power, the aggregate number drives up energy consumption.

Gartner projects that more than 50% of datacentres will exceed 6 kW per rack within two years; They expect that number to rise to 70% to 80% within four years due to the increased density of IT equipment, and that the ratio of power to cooling will hit 1:1. In addition, electrical costs per rack will increase by a factor of four, he calculates. Previously, the ratio was 0.5:1. The cost is basically unsustainable. IT must also begin to factor in costs for getting rid of end-of-life equipment. Disposal now has to be part of the TCO analysis.

The price tag includes not only the cost of safe disposal but the cost of ensuring that data is effectively removed from disk drives. A three-times overwrite is Department of Defense compliant, but you need at least a seven-times overwrite to be completely safe and 10 times is even better.

The cheapest option is to increase storage utilisation. You want to increase the utilisation of the spinning motors and platters that you already have Once the drive is spinning, additional utilisation essentially costs nothing from an energy standpoint.

Energy Tradeoffs

Trade-off Implication
Energy-efficiency vs. Performance More spindles boost performance but use more energy
Density vs. Cooling efficiency Cooling efficiency requires less density butwastes rack and floor space
High vs. Low disk speed Faster disks increase performance but burn more energy
Online vs. Offline (tape-based) data Online data is much more readily available but burns more energy
Energy vs. Capacity Small form-factor disks use less energy but require more spindles to achieve high capacity

Beyond consolidation, storage managers can deploy storage in more energy-efficient ways. If you don’t need high performance, deploy 7,200 rpm or 10,000 rpm disks rather than 15,000 rpm models, as the slower speeds use less energy. Similarly, smaller form-factor (2.5-inch) disk drives require only 5 volts vs. 12 volts for standard 3.5-inch form-factor drives. Small form factors, however, usually have smaller capacity.

Direct current (DC) can also be an energy-saving alternative. According to IDC, DC-powered equipment allows a portion of the heat load to move from the servers to the rectifiers, reducing heat at the system level by 20% to 40% versus a traditional alternating current (AC)-powered rack. DC offers some efficiency, but you’re mainly moving the problem someplace else.

Rearranging the datacentre

The cooling rule of thumb for raised-floor datacentres has jumped from 4 kW to 6 kW per rack. Beyond 6 kW, you can’t cool with just a raised floor. Today, a lot of gear is running over 4 kW per rack, which is getting close to the threshold. In response, large organisations are creating hot and cool aisles, and using blanking panels within racks to assist with air flow. Cool air is pushed into the bottom of the rack from the cool aisle and exits as hot air from the top of the rack into the hot aisle.

Offline savings

Another option is to move data offline. Tape not only costs less than disk but uses less energy and requires less cooling. An analysis of SATA disk and LTO tape, suggests the cost to acquire, power and cool a disk system is almost eight times that of a tape library. However this means giving up the performance of disk. After boosting utilisation, rearranging the datacentre and moving data offline, storage managers are left with replacing storage devices with more efficient devices. Some organisations have reduced their power consumption by 50% over the last few years by replacing old servers and consolidating DAS storage. However, energy consumption will probably go up as the organisations migrate to densely packed blade servers.

New tools and metrics

Some vendors are starting to provide tools that measure power consumption at the device level to manage energy the way they manage other aspects of storage. New energy metrics are also entering the storage lexicon. Kilowatt and kilowatt per hour are standard energy metrics. When applied to storage, you get kilowatt/terabyte. A more common metric at this point is kilowatt per rack. Due to increased density, datacentres today are pushing beyond 4 kilowatt per rack; by 6 kilowatt per rack, they’re getting into a heat danger zone.

An individual drive uses 5W to 15W of power depending on its capacity, rotation speed, form factor and operating state, but you can’t just multiply the number of drives in an array by some average power rating to get a total. The power consumption of the array is more than the sum of the power used by the individual drives. Controllers and other components consume power.

Storage managers also need to consider SAN switch power and cooling. Switches consume less power in the datacentre than servers or storage mainly because there are relatively fewer switches. Still, the power consumption of a switch is significant. A large switch will use 1,000W [1 kW] or more. Higher port density and performance increases switch power and cooling consumption. Don’t be surprised to see kilowatt per port and kilowatt per gigabyte per second metrics soon.

Energy bills — now running at $60 per square foot for the datacentre, according to Gartner’s Bell — currently go to the facility manager or chief financial officer, not to the storage manager. Datacentre space is handled by the real estate department. To lower energy costs, there needs to be more coordination among the disparate departments.

As energy costs and consumption rise, new tools — from low-power chips to digitally addressable power supplies that can regulate power to the device’s changing requirements — are being developed to more effectively manage energy. Power, cooling, space and disposal are becoming integral, closely watched parts of the TCO analysis for every storage device the organisation buys.