Green storage explained

Achieving energy efficient storage requires a well-thought out blend of products, and practices – held together by the right architecture

Escalating demands for storage and rising energy costs are creating a real headache for many storage professionals. According to Gartner, half of all datacentres will run into the limits of their power and cooling capacity this year. And by 2009, according to the analyst group, for 70% of the datacentres worldwide, energy will become the second highest operating cost.

Storage growth in some parts of the UK, most notably parts of London, is highly constrained (in some cases blocked altogether) by limits on premises' sizes and power supply – there is simply no more electricity to be bought at any price. In the face of this situation, storage managers must mitigate the rising cost of power and its availability by turning to the technologies and practices that can improve energy efficiency, which go under the banner of green storage.

This article explains the concept of green storage, examines issues arising in its deployment, looks at one user's experience of going green and considers the future of green storage practices.

What is green storage?

With the sheer volume of hype about green storage that has been flying around for the past 12 months, you could be forgiven for dismissing it as tree-hugging nonsense. But behind the vendor hyperbole there is in many cases a compelling proposition: that, by a combination of technologies, practices and policies, you can achieve reduced and more efficient energy use.

Businesses that do not pay attention to the issue will face unnecessary costs, says Clive Longbottom, service director with analyst firm Quocirca. "By not adopting green storage practices, a business risks higher energy costs for power and cooling plus higher-than-necessary equipment and management costs," he says. "They also risk slower response times, a need for more physical space than necessary and the likelihood of experiencing more failures and the need to carry a larger spares inventory."

Green storage is not a single product or system, and there is no single solution to reducing power demands or increasing power efficiency. Green storage is a strategy that should be adopted gradually through the purchase of more efficient products and by the adoption of practices which lead to better use of energy, cooling and space.

Approaches to green storage

At the component level, it is worth seeing whether you can switch to more energy-efficient kit. Since hard drives are always growing in capacity and becoming more power-efficient, one green tactic might involve replacing a series of existing 250GB hard drives with 750GB or larger devices. That way capacity is dramatically expanded but the actual number of drives stays the same, keeping power demands roughly unchanged.

Drive designs are also changing in response to the need for reduced power demands. Some drives support variable spindle speeds, allowing them to slow down when they're not being accessed. Hybrid drives include significant amounts of solid state memory on the drive itself, which reduces the frequency of platter access required and allows spindles to spin down more often.

Disk systems and arrays are also evolving. Controllers that use less power are being developed as well as systems that enable low-power options on large numbers of drives, by closing down RAID groups, for example.

There is also MAID (Massive Array of Idle Disks), in which the majority of disks are powered down at any given time. While MAID technology isn't recommended for online storage, it's useful for nearline and archival storage systems, although some experts question the total power savings and long-term reliability of drives within the MAID system.

Above the level of individual components there are further – software-based and supra-device – aspects to green storage.

Case Study:  BT Goes Green
BT has 23 datacentres in the UK and 70 in the rest of the world, with storage hardware predominantly from EMC and NetApp. It uses 0.8% of the UK's electricity generation. 

Its green datacentre plans are ambitious. It has reduced its carbon footprint by 60% since 1996 and has committed to reducing it by a further 80% by 2016. Given that, you would think that green storage was important to BT.

"I don't think it is," says BT head of datacentres Finlay MacLeod. "Our driver is based on the rising cost of energy, which has increased by something like 30% in the past couple of years. It is a variable cost and for that reason it's a good thing to get it under control. We also have to think of the likely introduction of the carbon tax liability," he says.
So, how is BT trying to achieve its ambitious targets for datacentre energy savings? The process starts when vendors are selected to tender, says MacLeod.

"When we are procuring IT hardware we ask the vendor about the energy consumption and heat generation. We ask what is the kilowatt per gigabyte rating and what maximum operating temperature the device will work at without risking damage," he says.

Given that air conditioning costs up to 50% of datacentre energy bills BT has taken an approach which tries to minimise its use. To this end BT has engaged with its suppliers, such as Cisco, HP and Sun, to get them to make equipment that will run hotter. For example, hardware for use in BT's software-driven telecoms infrastructure, the 21st Century Network, must be able to operate at 50 degrees Celsius, well above the 22 degrees Celsius datacentre norm. The company is also considering using winter weather cooling – circulating naturally cold air around its datacentres.

BT also uses more conventional but accepted techniques for improving cooling and storage efficiency, says MacLeod. 

"We use hot and cold aisles with curtains to control the flow and volume of air and have so far made a 16% saving on electricity," he says. "We also practice tiering of storage and move data from the highest performance disks to other media when appropriate."
For example, storage virtualisation allows storage administrators to provision storage to fewer physical drives and boosts utilisation levels. Thin provisioning allows storage capacity to be allocated on the fly instead of having to reserve disk space to specific applications in advance and have it sit unused until it is required.

There are also techniques that reduce the amount of data that needs to be stored, such as data deduplication which can reduce storage demands by ratios of up to 50:1. While deduplication has mainly been used in archive and virtual tape library systems, it is now appearing more frequently in primary storage settings.

Tiering of storage is another approach for maximising storage efficiency. Here data is matched by its importance to the most appropriate and cost-effective storage media. In this way, online data is moved from expensive, high-performance and power hungry media to slower, high-capacity nearline storage as soon as operational constraints allow.

"Tiered storage is all about planning what gets stored where," says Tony Lock, programme director with analyst firm Freeform Dynamics. "This has always been done – it's just that the 'green' aspect has highlighted the fact that continuously rotating high speed media isn't needed for all data."

Tiering can also take place internally to the hardware, such as with Pillar Data Systems' Axiom disk arrays, which allocate data to faster or slower moving parts of the same disk according to its importance.

At the highest architectural level, how efficiently you retain data comes down to knowing what information you hold and matching it to the performance and access characteristics of the hardware. Fundamentally this is a question of providing components of the storage architecture to match the lifecycle stages of your business's data in close conjunction with an ILM strategy, says Quocirca's Clive Longbottom.

"Without knowing what's already there, you have no chance of optimising its storage and all you will be able to do is fiddle around the edges," he says. "If you don't know what data you have out there, you cannot put together a coherent and cohesive management strategy."

Implementing green storage and measuring returns

Implementing green storage starts at the beginning of the procurement process and involves close scrutiny of the energy efficiency of products being considered. But it could also include – dependent on your business's corporate social responsibility policy – the entire lifecycle of the product and the greenness of its manufacturing, materials, transport and disposal. Key parts of that process should already be dealt with by the vendors as required by legislation affecting hazardous materials and their disposal, such as the RoHS Directive and WEEE regulations, says Lock.

"It is up to manufacturers to build according to local legal requirements," he says. "Disposal of old kit is another matter but increasingly it is an onus being placed on manufacturers."

When procuring storage products and attempting to determine probable ROI, you should compare them by meaningful criteria such as figures on energy consumption, such as IOPS per kilowatt, which you may be able to translate into figures directly correlating to the business like revenue per IOP.

Unfortunately there is no standard measure for energy efficiency that covers all storage devices, although for some products, such as storage switches, market competition has spurred vendors to battle it out using lab test figures (see product round up). Meanwhile the Storage Networking Industry Association is developing a labelling scheme, to be launched this year, to allow comparison of efficiency of energy use between hardware.

While chasing energy efficiency is a worthwhile cause, the objective is not to reduce the amount of kilowatts used for its own sake but to do that while retaining the optimum level of systems efficiency for the business. For example, reducing power consumption will save money on power costs, but if the total work performed is also reduced, any loss in revenue due to lost work – such as fewer IOPS – may cost more than the energy saved. The main thrust of green storage should not be to save money, but to maximise efficiency.

Future of green storage

On the technology front, we expect to see more energy-efficient hard drives, such as hybrid and fully solid-state drives, along with storage systems and controllers that actively monitor and manage power based on storage tier and access frequency. Expect also to see data reduction technologies such as deduplication and compression become standard features of storage systems as well as more application awareness being built into devices. As we move into the next decade, high-capacity, long-term storage needs could be fulfilled by holographic media.

At the architecture level, more and more businesses will begin to implement tiered storage as part of wider ILM strategies.

What is certain is that the aims of green storage will not go away. Energy supplies and space will continue to be squeezed and so it will always be good sense to work as efficiently as possible, says Hamish MacArthur, CEO with analyst group MacArthur Stroud. "Although there is plenty of hype around, the bottom line is that green storage is beneficial – the technologies and practices it comprises cut the cost of storage and the energy and space that it uses.

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