An evaluation of the power consumption and carbon footprint of a cloud infrastructure

The Information and Communication Technology (ICT) sector represent two to three percents of the world energy consumption and about the same percentage of GreenHouse Gas (GHG) emission. Moreover the IT-related costs represent fifty per-cents of the electricity bill of a company. In January 2010 the Green Touch consortium composed of sixteen leading companies and laboratories in the IT field led by Bell's lab and Alcatel-Lucent have announced that in five years the Internet could require a thousand times less energy than it requires now. Furthermore Edinburgh Napier University is committed to reduce its carbon footprint by 25% on the 2007/8 to 2012/13 period (Edinburgh Napier University Sustainability Office, 2009) and one of the objectives is to deploy innovative C&IT solutions. Therefore there is a general interest to reduce the electrical cost of the IT infrastructure, usually led by environmental concerns. One of the most prominent technologies when Green IT is discussed is Cloud Computing (Stephen Ruth, 2009). This technology allows the on-demand self service provisioning by making resources available as a service. Its elasticity allows the automatic scaling of the demand and hardware consolidation thanks to virtualization. Therefore an increasing number of companies are moving their resources into a cloud managed by themselves or a third party. However this is known to reduce the electricity bill of a company if the cloud is managed by a third-party off-premise but this does not say to which extent is the power consumption is reduced. Indeed the processing resources seem to be just located somewhere else. Moreover hardware consolidation suggest that power saving is achieved only during off-peak time (Xiaobo Fan et al, 2007). Furthermore the cost of the network is never mentioned when cloud is referred as power saving and this cost might not be negligible. Indeed the network might need upgrades because what was being done locally is done remotely with cloud computing. In the same way cloud computing is supposed to enhance the capabilities of mobile devices but the impact of cloud communication on their autonomy is mentioned anywhere. Experimentations have been performed in order to evaluate the power consumption of an infrastructure relying on a cloud used for desktop virtualization and also to measure the cost of the same infrastructure without a cloud. The overall infrastructure have been split in different elements respectively the cloud infrastructure, the network infrastructure and enddevices and the power consumption of each element have been monitored separately. The experimentation have considered different severs, network equipment (switches, wireless access-points, router) and end-devices (desktops Iphone, Ipad and Sony-Ericsson Xperia running Android). The experiments have also measured the impact of a cloud communication on the battery of mobile devices. The evaluation have considered different deployment sizes and estimated the carbon emission of the technologies tested. The cloud infrastructure happened to be power saving and not only during off-peak time from a deployment size large enough (approximately 20 computers) for the same processing power. The power saving is large enough for wide deployment (500 computers) that it could overcome the cost of a network upgrade to a Gigabit access infrastructure and still reduce the carbon emission by 4 tonnes or 43.97% over a year and on Napier campuses compared to traditional deployment with a Fast-Ethernet access-network. However the impact of cloud communication on mobile-devices is important and has increase the power consumption by 57% to 169%.