Subram Natarajan: Going green with storage

More than ever IT companies are facing the need to address the environmental issues arising out of power consumption and cooling. Faced with increasingly urgent warnings about the consequences of the projected rise in both energy demands and greenhouse gas emissions, governments and businesses alike are now focusing more attention on the need to improve energy efficiency.

Even from an IT perspective, the environmental issues can potentially impede the capability of IT to grow and support the business demands. CIOs today are being challenged to rethink their data centre strategies, adding energy efficiency to a list of critical operating parameters that already includes serviceability, reliability and performance.

Storage servers form an important element of the infrastructure chain. Power scarcity will be part of the storage landscape for the foreseeable future "� according to IDC, by 2008, the budget allocated for keeping the data centres cool will exceed the investments made for servers and storage. Although storage products are not the worst offenders of this cause, it is still an important contributor.

Transitioning to an environment where the servers and storage are optimised for energy and operational efficiency can be a complex undertaking. There are multiple components to factor into the equation and best results can often be achieved by integrating improvements on multiple fronts. The good news is that there are many solutions and techniques available to support such a transition. Also, the process can occur in a step-wise manner, reducing risks and helping to realise benefits along the way. This article outlines the challenges facing us and the possible solutions.

The uncomfortable truth

A recent study conducted by IBM indicates that the heat load per product footprint is the highest for communication equipments. Over the past 15 years, power consumed by disk based storage equipments has steadily grown from 200 watts per sq ft of equipment in 1992 to about 1,100 watt per sq ft today. Tape systems are considered to be most energy efficient devices "� today they consume about 200 watt a sq ft of equipment. Although the past 5 years saw a dramatic reduction in power consumed per GB storage "� from about 1 watt per GB in the year 2000 to about 0.5 watt per GB today, the rate of storage consumption remains high, leading to higher energy consumption.

With the ever increasing storage density and capacity consumption, it is quite possible that storage can become one of the highest power demanding infrastructure element. Therefore it is important for every IT leader to plan energy efficient techniques in their strategy.

From a business perspective, the challenges are self-evident: energy costs are rising, supply is limited, the data centre infrastructure is being taxed, and its ability to meet business demands is at stake. Addressing these problems comprehensively means that we will need to focus on data centre innovation. Fortunately, green strategies and technologies exist today to help optimise space, power, cooling and resiliency while improving operational management and reducing costs. This will help enable companies to grow and meet the expanding business needs.

Transitioning to green storage

How do you go about creating an energy-efficient green storage? Based on all the learning from operating data centres, several well established IT vendors have spelt out what works and what doesn't. The technologies and strategies for improving storage energy efficiency span the entire data centre ecosystem. Companies typically achieve the best results by integrating power and cooling changes with advanced technologies such as virtualisation, energy efficient hardware and software, and power and workload management initiatives.

There are three simple techniques to making the storage green

"� Cool storage more efficiently

"� Deploy more power efficient storage

"� Utilise storage more efficiently

Cool your storage more efficiently

Within a data centre, usually there are a few areas where the temperature is high (hot spot) than the rest. To compensate for this hotspot, the current common practice is to lower the overall inlet air temperature. This leads to inefficient energy use in the data centre ecosystem. In order to address this problem, experts believe that the most productive first step is to conduct a best practices assessment and energy audit. There are tools and techniques that are available to identify the hot spots within the data centre. Using the profile outlined by such tools, a careful review and assessment will help strategise on what immediate actions can be taken to drive maximum energy efficiency in the data centre.

Many a times, simple rearrangements in the air inlet (such as moving the perforated tile closer to hot spots) or even repositioning the racks within the data centre can help alleviate the hotspot. Studies indicate that reducing the hotspot temperature by approximately 10 °C improves cooling efficiency by 2.5. Such systematic checkups offer a real-time profile and model of the data centre's energy use conditions and make it possible to pinpoint areas of high energy use, while establishing a baseline for further planning.

Using more efficient cooling technologies such as rear door heat exchangers works well for servers and storage "� they help in reducing the heat output from the infrastructure equipments. Most data centres already have begun to deploy some form of water cooling. Extending the same thought, we can use it to cool racks because water based heat exchangers for racks are more efficient. Practitioners believe that up to 55% of heat can be effectively removed by using rear door heat exchangers.

Deploy more power efficient storage

Physical factors of a disk that affect heat energy dissipation from storage are essentially the density and the speed. The heat output is proportional to density and speed of the disks. This means, faster disk spindles generate more heat that the slower ones. Apart from the heat factor, a similar trait exists with power consumption as well. For example, the power consumed by a 300 GB disk at 15,000 RPM is approximately 0.062 watt/GB, whereas if the speed were 10,000 RPM, the power consumed is about 0.039 watt/GB. This effect will be more pronounced for disks with lower capacity.

IT leaders should make it a practice to constantly reevaluate whether the storage medium used are indeed the best from a power consumption stand point. Keeping in mind that idling disks also consume power "� albeit less than when performing Read/Write operation, it becomes all the more important to consider placing data on slower disks. It is in this regard, tape based storage should be strongly considered as an alternative wherever practical. As capacities grow the relative power consumed during a typical read/write operation by tape will prove tremendously advantageous (25:1) over even slower disks.

Yet another point to consider is frequency with which storage devices are refreshed. Older storage devices tend to waster more power because of lower operating efficiencies. Considering a modest 30% per year storage density improvement, the efficiency opportunity of 3 year retention is almost twice that of a 5 year retention period. Hence, one should consider refreshing or replacing older hardware as frequently as permissible by the business and IT demands.

A natural extension of this discussion will lead us to Information Lifecycle Management. Technologies such as virtualisation allow us to create virtual pools of storage that differ in capacity, performance and energy attributes. Using virtualisation technology to move data from one storage device to another, based on the business and energy requirements can now occur on demand and without application disruption.

Utilise storage efficiently

The principles associated with Information Lifecycle Management apply to energy conservation also. Understanding the nature of existing data and placing them on the appropriate devices will increase the efficiency of storage. Therefore, business leaders and IT leaders alike should constantly look for opportunities to perform data rationalisation. More often than not, a periodic assessment will reveal that a lot of existing data may be duplicate, unused, inactive and/or temporary. Based on the corporate governance, business and regulatory requirements, all such data must be handled appropriately.

Technologies such as automated space reclamation can help increase space utilisation. The idea with this technology is to periodically scan the file system for any free blocks resulting from file/data deletion. Then these blocks are added to the block allocation list thereby resulting in less wastage and fragmentation. Virtualisation and hierarchical storage management can help define policies based on which data can delete upon expiry.

Data de-duplication solution when deployed appropriately can go a long way in enhancing the efficiency. Common implementations of this technology use hash values of data blocks to identify duplicate values. In addition, simple data compression technology can also help with storage space savings.

Whose job is it?

Until recently, environmental management and energy expenditures were typically the responsibility of facilities departments. But rising energy costs and evolving IT demands are changing all that. It's becoming critical that the facilities and IT departments form a partnership and collaborate in this area. Even then, many companies will not have the skills or the tools to profile and model thermal conditions and appropriately apply the information to data centre planning or upgrades. Because these are highly specialised skills, obtaining outside help during this part of the process may be well worth the investment.

To conclude, as governments and corporations intensify their focus on reducing energy demands and greenhouse gas emissions, pressure to improve data centre energy efficiency will continue to grow. As outlined in this paper, there are opportunities in existing setups that will help contain the power and cooling issues arising out of storage devices. Simple techniques such as those that were discussed in this paper can go beyond just addressing the environmental issues "� they bring operational efficiency and help improve the utilisation levels of various infrastructure elements.

Successful IT leaders will make these techniques as part of their strategy and operation. And in doing so, their ongoing efforts to think green will help keep their companies operating in the black.

The writer is a senior consultant, systems storage group, Asia Pacific at IBM Global. He can be contacted at subram.natarajan@in.ibm.com