Under Pressure - Rising Densities
Datacentre Dynamics Focus - June '09
The challenge for data centre professionals today is in getting the maximum from the space available by increasing the number of high-density racks. But can airflow alone cope with the cooling challenges of high-density computing?
No standards body has yet offered a universally accepted definition of 'hig-density computing'. Despite a slight fuzziness about what it actually is, high density is clearly an important goal for data centre professionals, and represents a clear trend towards which the industry is moving.
Victor Avelar, senior research analyst with Schneider Electric , defintes it thus:"High-density computing is about packing as many servers, typically blade servers, as you can into a data centre rack," he says. "the more power per unit of rack space that goes ito the rack to support the increased processing power of modern servers, the denser the rack."
He says that today's typical desnity of two-to-three kilowatts (kW) per rack is heading for the history books:"Densities are rising to the five to eight kW per rack range as a result of virtualisation and consolidation of servers," he believes. "The higher density racks are already in the 10-20kW range."
The motivation to squeeze the maximum from the space available in a data centre is clear. Data centre managers and the enterprises that rely on such facilities are being pushed to achieve more performance at greater value for money, and to reduce energy demands for both environmental and cost reasons.
"Enterprises have moved to consolidate their data centres and to work out how to avoid energy efficiency taxes that will apply in 2010," says Jeremy Young, director for service management and automation solution sales at Computer Associates. "Basically Defra (the Department for Environment, Food and Rural Affairs), will be introducing tax on those consuming more than £500,000 in energy each year. All this is increasing the desired density of an organisation's computing infrastructure."
But good intentions and carefully laid plans aside, are high-density principles actually being adopted in the real world?
"Enterprises are taking virtualisation strategies step by step, as they can result in complex management requirements," says Young. "I don't think enterprises are setting out to organise high-density computing as such: it's more that businesses are changing shape, and they know they can save money by consolidation and so end up with higher density computing almost as a by-product."
But organisations that are tempeted to look at computing capacity benefits without considering wider operational costs and constraints should think again, warns Young.
"Companies may consolidate for their data centres, but they can't consider components discretely," he advises. "When a company is reducing costs and boosting server utilisation it is inevitably increasing energy use and cooling needs for the infrastructure, so new heating, ventilation and air-conditioning systems will probably be needed."
He says there are vendors, including CA, that have tools to help manage a virtualised data centre infrastructure and that better understand energy consumption in a rounded, end-to-end way.
"We're doing more high-density data centres that traditional ones at the moment, and a lot that are medium desnity of about 10kW," says Chris Smith, sales and marketing director at data centre infrastrcuture specialist on365.
Some centres are at a hlaf-way stage:"You have data centres that are mostly on traditional lines that have a high-desnity 'room within a room', says Smith. "Wherever you have high density, you have a challenge with delivering power. But power us the easy challeneg - it is the cooling process that's hard."
"When a high-density rack is running hard, a lot of air is being drawn in. We offer hot aisle containers that enclose part of the operation, managing the hot air out and cool air in."
Avelar agrees that cooling - specifically the cost of cooling - is the primary challenge as data centres move to achieve maximum efficiency from available space. "Cooling is the biggest issue when it comes to deploying high density," he believes. "Most traditional data centres have raised floors and use the raised floor as plenum. Cool aire is forced under the floor by air handlers and gets fed to the servers through perforated floor tiles. Given that there are practical limits in achieving per-tile airflow above 300 cubic feet per minute (cfm), there are challenges in properly cooling high-desnity enclosures.
"With the rack filled with blade servers in a 42U configuration, requiring 20kW of power, the requirements would be 2,1000cfm per rack. This would require seven vented floor tiles per rack, whih is eight times more than what would normally be allocated. To achieve this would require substantial increases in both aisle width and spacing between the racks - which can be expensive," Avelar says.
Built into all future thinking on density and data centre design must be the ability to take a flexible approach that takes account of particular needs at a a particular time, says Smith. He cites the example of a data centre fitted by on365 that runs the BBC iPlayer service: "It is able to cope with huge demand at particular times of the day," he says.
"It's about data centres offering a flexible approach to maximise levels of efficiency. For the data centre itself, it's about maximising the returns you get from the space you have."