Behind the racks of servers lining the aisles of ever-expanding data centres you will find one or more boxes connecting the power cables. Easily overlooked and widely misunderstood, if you removed these small but critical components the whole system would fail. They are the Power Distribution Units, or PDUs.
As the name suggests, a PDU distributes energy across the racks, servers and networking equipment located within the data centre. There are two types of PDU: basic and intelligent. Basic PDUs provide straightforward power connectivity and routing for all the IT components. Intelligent PDUs sit within the rack actively monitoring the environment and looking for threats from electrical circuit overloads or any physical and environmental conditions that might place critical IT computing loads at risk.
External trends such as the rapid rise in the volume, big data, virtualisation and cloud computing, as well as the internal need to deliver a reliable, secure and flexible service, are putting increasing pressure on the way data centres operate.
In most cases, the power supply and distribution across the data centre cannot afford to be a passive process. The ever-changing use of technology, equipment and operating policies are creating increasingly variable power and environmental demands at the rack level. The PDU needs to become ‘smart’, able to monitor, analyse and respond to real-time threats and opportunities.
Intelligent PDUs provide data centre and facilities managers with the comprehensive, accurate energy measurement data they need to make the most efficient use of power resources, inform capacity planning decisions, improve uptime, measure PUE (power usage effectiveness) and drive green data centre initiatives that could save energy and money.
Studies by McKinsey & Co and Gartner Research revealed recently that only six to twelve per cent of the electricity consumed by most data centres is used to power active servers. It would seem that many data centres are responding to demands for service reliability and security by diverting as much as 90 per cent of their electricity to ensure availability of idle servers in fear of unforeseen downtime. Such environmental wastage is increasingly unacceptable when an alternative approach is so readily available.
Some intelligent PDUs offer companies the option of switching individual or group outlets on or off in response to real time needs, negating the need for permanently switched-on stand-by and creating a far more cost-effective alternative to a complete data centre retrofit. The most effective new generation of intelligent PDUs comprehensively monitor power and energy consumption to within a one per cent billing grade accuracy. Some even incorporate Circuit Breaker Status Monitoring, which provides active monitoring and alarming of the circuit breaker on/off status. Some designs even measure these electrical attributes at the individual equipment level to allow users the most advanced planning data and energy optimisation opportunities.
One important feature to consider when looking at an intelligent PDU is the ability to easily raise the temperature of the data centre by as little as one degree, to help create huge savings made on energy costs without putting operations at risk. In fact, the recent ASHRAE (the American Society of Heating, Refrigerating and Air-conditioning Engineers) third edition of the ‘Thermal Guidelines for Data Processing Environments’ suggests that data centre managers should extend the recommended ranges for IT equipment to allow for aggressive economisation. But this is only possible with technology engineered to enable this flexibility – most basic PDUs are rated to only 40 or 45 degrees.
Most PDU designs have no user serviceable parts. In cases of electronics failure or desire to upgrade the core intelligent management function, the entire PDU must be replaced. The latest, leading edge PDUs offer full hot-swapping capability of the network intelligence module, so that the PDU can be replaced or upgraded by in-house teams without interrupting vital power supply.
From an external physical perspective, an intelligent PDU must combine ease of use with maximised performance. It is becoming apparent that PDUs with an ultra-slim chassis and low profile circuit breakers best enable users to access other components within the rack, reducing crowding and interference. The physical size of the PDU is often overlooked until a critical event highlights the utility of this core attribute. Take for instance a hot-swappable fan, power supply, or network card in many blade or large form-factor rack mount equipment; in these cases, a large rack PDU can interfere with the removal of these server components and physically prevent hot-swapping in times of equipment maintenance.
Other external features that data centres should look for in an intelligent PDU include a large LED display, locking outlets, field rewireable input cords, adjustable tool-less mounting and colour-coded outlets and breakers. These features help data centre technicians to simplify installation, avoid errors during installation and maintenance, and create a cleaner, customised installation fit without hassle. This improved accuracy is an important factor as studies estimate around 30 per cent of downtime is due to human error.
The UK Carbon Reduction Commitment (CRC) and European Union Energy-Using Product (EuP) are increasing the pressure on data centres to measurably reduce the energy used and carbon produced by their IT facilities. PDUs can help data centres achieve this goal.
Of course, it is not just a question of installing the technology. It also requires a change of employee mind set. Powering a data centre is perhaps not the same as boiling a kettle or putting the washing on, but the same principles apply: understand your power needs and usage and adapt to optimise them. PDUs provide data centres with a unique opportunity to achieve this – don’t let that opportunity pass you by.
Mike Jansma, co-founder, Enlogic
