condition the power received from supply source and will filter out transients and other fluctuations, thereby providing the IT hardware with invaluable protection against damage. Power protection also provides for
controlled shutdown and smooth start up of servers, functions that are essential in systems where it is accepted that hardware will, from time to time, go down.
Zombie servers Well-designed power management also guards against `zombie servers.’ These are machines that are functioning intermittently or erratically, but have not quite failed completely. Because their behaviour is
unpredictable, zombie servers are a potent source of instability and data loss in IT installations. A good power management system will `fence’ the zombie servers, isolating them from the rest of the installation, and then power them down. There is another crucial reason
why power protection and power management are essential in systems where resilience is provided at levels above the hardware level. For these higher level resilience
strategies to work, the level or levels at which the resilience is provided must always be power aware - that is, they must always know the current status of the power supplies, and this information can only be provided by a power management system. If the mains supply fails, the UPS will support the local servers for, say, 15 minutes, which is more than adequate time for the migration of the virtual servers to take place. But if the power system has not
informed the virtualisation manager that the installation is now running on battery power, how will the migration be initiated? It should now be clear that power
protection and power management are at least as important with converged/ virtualised infrastructure as they are in more traditional IT environments and that, in converged/virtualised environments, the power management system must be closely integrated with
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the virtualisation management software, to ensure fast, automatic response to faults. There is, however, another important
issue to be considered when providing power in converged/virtualised environments, and that is load fluctuation. New power usage optimisation
techniques in IT hardware as well as on the cloud and virtualisation layers mean that the load on the power system can vary widely and rapidly. Although the variations are often
cyclic, in some cases they can be instantaneous and erratic. Unless the power system has been designed with these variations in mind, the result is almost certain to be poor energy efficiency.
Multiple UPSs Fortunately, there is a solution to this problem: specify a system made up of several UPSs which share the load, and which are complemented by intelligent multi-UPS management system. This software is designed to ensure
that, at any given instant, only those UPSs needed to meet the current power demand are operational. The other modules are held in a standby state where they consume almost no power. The management software can,
however, bring them back into service almost instantaneously - typically in less than two milliseconds - when the load increases. This very fast transition is invisible to the equipment powered by the UPSs. This arrangement means that the load is concentrated on the minimum number of UPSs needed to meet it and that, as a consequence, these UPSs are well loaded and will therefore operate efficiently. With the best hardware it is, in fact,
possible to take this multi-UPS approach even further, by specifying UPSs that are themselves made up of modules that can be instantly transitioned between standby and operational mode. Such an arrangement, which is usually described as a module management system allows the UPS power capacity to be accurately matched to the power demand over a
Controlling power management using effective IT
very wide range of loadings, ensuring that high operating efficiency is achieved under all operating conditions, irrespective of load fluctuations. Proven and cost-effective power
technology that meets all of these requirements is available now and is, indeed, already in widespread use around the world. Powering converged infrastructure
does not, therefore, need to be complicated or challenging, provided that you choose a supplier with the right experience and expertise.
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NETCOMMS europe Volume IV Issue 3 2014 21
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