In the fast-paced world of corporate IT, cloud computing is no longer the reserve of early-adopters. The principles behind real-time delivery of IT infrastructure, services and software over the internet or an internal web-based infrastructure are now readily accepted, and organisations of every size and description are rapidly adopting outsourced software, platform and infrastructure solutions in order to drive efficiency up and costs down. Despite this, one area that is still overlooked is the impact that cloud computing has on IT infrastructures. Here, Tatu Valjakka of Eaton, examines the unique power, cooling and availability challenges presented by cloud computing and outlines some strategies for optimising an IT infrastructure accordingly

Power and Cooling

Maintaining availability and providing adequate power and cooling are long-standing challenges for traditional data centre managers. However, addressing those issues can be even harder for managers of cloud data centres.

The server hardware that most cloud infrastructures use to host virtual machines is bigger and more robust than a typical single-function server. It’s also far more heavily utilised with the average virtualisation host server running at as much as 80% of processing capacity at any one time, compared to just 5-15% for the average non-virtualised server. For both reasons, the virtualisation host servers in most cloud data centres demand more power than conventional servers and put greater strain on power distribution units (PDUs), panelboards and uninterruptible power supplies (UPS systems).

This is particularly true when organisations use blade servers to host their virtual machines. Blade servers utilise multiple plug-and-play processing units that share common electrical feeds, power supplies, fans, cabling and storage. Such an arrangement conserves data centre floor space, simplifies hardware management and enhances IT flexibility. However, it also significantly raises compute densities. Subsequently, blade servers generate enormous amounts of heat and radically increase rack-level power requirements. A typical rack full of blade chassis can draw as much as 30 kW - more than many power and cooling systems can handle.

But, IT and facilities managers can meet the challenges of providing power and cooling to cloud computing environments by implementing certain strategies. For example, rather than wasting time, money and resources deploying excess capacity in advance of future requirements, modular power system components can be used. These allow capacity to be added quickly and incrementally as the need increases. Moreover, rack- based modular power system components tend to be compact and easy to install, making them an ideal fit for fast-paced cloud data centres, in which technicians are constantly moving, changing and adding infrastructure resources.

For cooling, modular cooling systems can provide an alternative to the traditional Computer Room Air Conditioning (CRAC) or ‘hot aisle-cold aisle’ hardware configurations. However, deploying additional cooling blocks as needs increase is not as simple as with modular UPS systems as they require installation of under-floor or overhead piping for those units in advance. As a result, many companies prefer to reduce cooling-related power consumption by equipping their CRAC and computer room air handler (CRAH) systems with variable frequency drives or electronically commutated (EC) fans.

Companies looking for lower upfront costs and higher operating efficiencies can install passive cooling systems. These employ enclosures equipped with a sealed rear door and a chimney, which captures hot exhaust air from servers and vents it directly back into the return air ducts on CRAC units. The CRAC units then chill the exhaust air and re-circulate it.

Large data centres like those that supply public cloud services often house UPS equipment in a dedicated facility room adjacent to the server floor. Setting up two facility rooms, one for UPS and power system electrical components and the other for UPS batteries, can be an even more efficient arrangement. While UPS electronics can typically operate safely at 35°C/95F, UPS batteries must usually be kept at 25°C/77F.

Placing UPS batteries in their own environmentally-controlled room reduces the amount of heat the cooling systems must handle.

Reliability

Another issue to be considered when optimising an infrastructure for cloud computing are the implications the heavy use of virtualisation can have on availability. In a traditional data centre, each server typically supports one application. In a virtualised cloud computing data centre, a given host server may support a dozen or more applications. Any time a host machine fails, therefore, it has the potential to impact large numbers of users and business functions. Moreover, the flexibility that helps make cloud computing and virtualisation so attractive can also inadvertently produce downtime. Without proper administration, shifting workloads suddenly within and across data centres can result in overloaded circuits or overtaxed cooling systems, which can in turn bring down critical systems.

Though cloud computing can make preserving uptime more difficult, some practices and technologies can significantly ease that task. For example, organisations planning to add a cloud infrastructure to an existing data centre should have a thorough power chain audit. When conducted by a certified power system engineer, a power chain audit can help evaluate power systems and determine which, if any, should be upgraded, augmented or modernised to support a cloud environment.

Organisations can also increase availability and reduce the likelihood of unscheduled downtime by utilising a redundant power system architecture. An N+1 architecture, suitable for small or medium cloud environments, includes one more UPS, generator or other power component than the minimum required. Thus, if any one component experiences an outage or requires maintenance, the remaining systems can still provide adequate protection against data loss. For large cloud environments, 2(N) architectures feature two separate but identical power paths.

Under normal conditions, both paths share the load evenly. Should one path experience planned or unplanned downtime, however, the other can compensate by temporarily running with the full load.

To further improve reliability, cloud data centre managers can use software-based redundancy techniques such as replication to continuously capture changes as they occur on protected servers and then replicate them in near real time to backup servers. Another effective software-based reliability strategy capitalises on the live migration functionality built into many server virtualisation solutions. Live migration systems like VMware’s vMotion solution enable administrators to move virtual servers almost instantaneously from one physical host to another in response to technical issues or maintenance requirements.

Clean, dependable power is as critical to the successful operation of cloud infrastructures as processing capacity and storage space. In order to keep a cloud data centre running smoothly, then, administrators need complete, up-to-the-minute information about the status of both their IT resources and their power resources. Today, many cloud operators use separate management tools to monitor their server and power environments. However, integrated solutions are now available that allow administrators to manage physical servers, virtual servers, UPSs, PDUs and more all through a single console. For example, Eaton’s Intelligent Power Manager (IPM) software and VMware’s vCenter Server virtualisation management system work together to provide a comprehensive view of network- and power-related events and alerts in one place. What’s more, administrators can configure the two systems to act on status information dynamically. Indeed, IPM can trigger vMotion to transparently move virtual machines from a server affected by a power interruption, to an available server on a network, before gracefully shutting down affected servers before the UPS systems run out of battery power.

Cloud-based software, platform and infrastructure solutions improve the efficiency and elasticity of IT operations but also subject data centres to significant new pressures. To master these challenges, organisations should adopt technologies and techniques that increase the reliability and redundancy of their physical and virtual environments, including power and cooling systems. By doing so, any company can enjoy the power of cloud computing reliably and cost-effectively.