Power Monitoring in the Data Centre: Is the Right Time Now? Jacarta Ltd www.jacarta.com
Power Monitoring in the Data Centre: Is the Right Time Now? Introduction Data centre power monitoring has been much discussed over recent years but without necessarily providing IT Managers with real, practical answers to many of the key questions. This paper, by exploring the answers to these questions, is designed as an aid to IT Managers wrestling with the problem of whether to implement power monitoring, what the likely benefits will be, and how to practically implement a power monitoring solution with minimal or no disruption to daily operations. 10 Key Questions 1. How can I reduce the power usage in my data centre? In order to move towards reducing power consumption in a data centre, the power in that data centre must first be monitored, recorded and assessed. This can be an extremely time consuming and costly process and potentially self-defeating if not carried out efficiently. Once some sort of mechanism is in place to enhance IT Managers understanding of the overall power consumption picture, opportunities will present themselves to obtain power usage reductions over time. If power monitoring can be carried out down to rack level, this provides the user with both the ability to make an assessment of what is happening within that rack and the capacity to make comparisons with other racks in the data centre. 2. Which racks in my data centre are using the most power and are the most expensive to run? Monitoring the input supplies on each individual rack will enable users to easily identify which racks are the most costly to run, and which the least. This comparison process can be invaluable in terms of providing a platform to focus on the areas where cost savings may be most easily obtained. Voltage data can be obtained although this is relatively straightforward as it should be fairly constant across the data centre as a whole, especially if power is supplied via a true online UPS. However, the collection of current data (amps) will be crucial to gaining a clear understanding of the variances in power consumption from rack to rack. A useful ratio to use when comparing rack power usage is A (where A is the total current draw of the rack) U (where U is the total amount of U space utilised in the rack) This ratio helps us to make comparisons between different racks irrespective of the amount of capacity utilised in each rack. So for instance: Rack 1 has a total current draw of 24A and U space utilisation of 22U. Rack 2 has a total current draw of 25A and U space utilisation of 30U. AU Ratio for Rack 1 = 1.09 AU Ratio for Rack 2 = 0.83
Rack 1 is clearly more power hungry than Rack 2, despite less U space utilisation. The average AU of all the data centre racks can be calculated as soon as monitoring of the total current (A) into each rack is available. Equipment can subsequently be added or taken away from racks in the future and more racks introduced, but the recalculated average AU figure will provide a straightforward means of proving that power usage is becoming more efficient over time, even if total power usage for the data centre increases. The Power Usage Effectiveness (PUE) ratio that is now used widely throughout the IT industry, is extremely useful as an overall measure of the power efficiency of a data centre. However, it is very difficult to use this ratio to compare the power efficiency of one data centre to another, as each and every data centre is different. Some may be running at full capacity, whilst others may be running at considerably less than full capacity. Space constraints (or otherwise) and the nature of the environment itself (the location, nature of the building, etc.) will all contribute to a data centre s PUE. Similarly, it is very difficult to compare the power efficiency of one rack to another but rack power monitoring and the adoption of the AU ratio, do provide a basis for recording and mapping power data over time with a view to achieving significant power usage reductions in the future (and proving that these power reductions have been achieved). 3. Can I reduce the power consumption in my data centre racks? The answer to this question, of course, is Yes, except that it will be possible for the total power consumption to actually increase where spare rack capacity has yet to be utilised. However, as long as power data is being recorded, there s no reason why the AU ratio cannot be reduced. 4. Can I assess whether it is more economical to invest in newer, less power-hungry IT equipment rather than continuing to run my existing equipment? Without the relevant power data, there is no way of knowing what the real power saving benefits will be of implementing new equipment. Power rating plates and specification information may not necessarily provide a reliable means of assessing the real power usage of a particular piece of equipment in site-specific operation. However, as soon as the before and after data can be captured, then it becomes very possible to gain visibility of the economic benefits or otherwise of implementing newer equipment from the power perspective. 5. Can temperature in the data centre be safely increased to help reduce air conditioning and air handling running costs? The hope, of course, is that by raising the temperature, even by very slight amounts, that power usage by the air conditioning and air handling units will be reduced. In order for this process to be successfully carried out, temperature should be monitored throughout the data centre, and ideally within each rack. As data centre cooling can make up such a high percentage of overall data centre power usage, the relationship between temperature and power is a critical one.
It can be extremely difficult to decide on what the optimum temperature level is for a particular data centre or server room, especially as different parts of the room and individual racks may be generating more heat than others. The beauty of being able to monitor power down to rack level is that it gives us the opportunity to see what effect, if any, the increase in temperature level has on the power usage in racks: If the power usage is higher this may point to an increase in the activation of server fans or rack fans, for instance. If this increased power usage is happening across multiple racks, it may very well negate the potential savings from running the room temperature at a higher level. Monitoring the rack power, together with temperature, provides us with the opportunity to safely see the effects of raising the temperature without compromising system availability. 6. Can I build up a clear picture of power usage over time that will enable me to reduce my AU ratio and running costs? There are likely to be some eye-opening findings once rack power monitoring is invoked. However, the real benefits will become more evident over the medium to long-term. As more and more relevant data is gathered, day-to-day decisions regarding the network infrastructure can be taken that involve power usage and the associated costs. If a power monitoring device is SNMP compliant, network management systems can be used to ensure that the power data needed is regularly recorded, stored and available for later analysis. However, if the network is expanding, it may be extremely difficult to reduce overall running costs, although it should still be possible to improve the AU ratio over time. 7. What effect do internal computer fans have on the AU ratio? The AU in any given rack will increase if server fans are active and the extent of the increased power draw can be evaluated by monitoring rack power. Internal server fans can use upwards of 10% of the overall power used by a server. Servers with fans that are controlled thermostatically increase fan speed as more cooling is needed and this, in turn, increases the power needed by that server. Rack power monitoring presents IT Managers with the opportunity to gain a clear understanding of the relationships between CPU usage, data centre (and rack) temperature, and power usage. Informed judgements can then be made as to whether it is more economical to reduce the overall room temperature for instance, or implement other mechanisms for reducing power usage such as improving ventilation and airflow. Power monitoring down to rack level may also be the only way of knowing that internal fans are actually becoming operative at all. That information alone could be extremely valuable in terms of understanding what is happening to the power in that rack and how best it can be managed to minimise costs. 8. Can I reduce power usage without compromising network operations? In a static world, the implementation of newer, more power efficient equipment will ultimately result in a reduction in AU. If reductions in the power used to drive rack peripherals (eg. fans in legacy racks) can be achieved, the AU will decrease also.
As knowledge surrounding rack power usage increases, so the capacity of the IT manager to implement power reductions will increase also. A sufficient understanding of the power usage situation will ensure that AU reductions will not compromise network availability. 9. Is it possible to be notified immediately about significant changes in data centre power and environmental conditions that may otherwise have serious repercussions for network availability? Monitoring devices are now equipped not only to monitor a variety of sensors (power, temperature, humidity, etc.), but they also have the capacity to provide management personnel with immediate notification should abnormal conditions occur. For example, an over-voltage alarm condition may be cause for concern and need to be investigated further, whilst a high temperature alarm could signify air-conditioning failure. Alerts can typically be provided via email, SMS or SNMP. 10. Can a solution to all the above questions be adopted without disruption to the existing network infrastructure and without downtime? Monitoring devices and sensors are now available that can be installed without any downtime. Intelligent PDUs can be installed in racks but the power to the equipment obviously needs to be removed in advance. Unobtrusive sensors that clip round the 16A or 32A input power cable are now available to monitor the current draw within racks. These eliminate the need for network downtime during installation and provide an extremely practical and cost-effective way of implementing power monitoring. Caution will, of course, still need to be observed as usual when running sensor interface cables. Summary Knowledge is power but, ironically, without monitoring power the appropriate decision making knowledge won t exist. It s very unlikely wholesale changes can be made immediately to data centre IT equipment or facilities that will have a significant impact on power usage. However, over time, with suitable data available, informed decisions can be taken that will result in significant data centre power savings. Rack power monitoring enables that data to be collected and utilised in a practical way to facilitate those savings. To ensure IT Managers have the most appropriate data to make informed decisions regarding power usage, environmental monitoring and power monitoring should be carried out alongside each other in the data centre. Power sensors such as the Jacarta intelliamp current sensor are available that can be installed without the need for downtime or disruption to the network, ensuring that power monitoring solutions can be implemented quickly and cost-effectively, irrespective of the age and nature of the data centre. Implementation is best carried out by specialist resellers that have independent access to the required knowledge, tools and products that most adequately suit a customer s power monitoring requirements. See also: Jacarta White Paper: RMS versus Mean: The Importance of True RMS Power Monitoring