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Energy efficient data storage – deployment of efficient technologies and solutions in data centres

Data storage is central for any business application and it is therefore not surprising that storage growth is expected to increase by 60% per year through 2020 [1]. As data storage is also expected to be responsible for a significant part of the energy consumption in data centres over the next years, it is crucial to make storage systems more energy efficient. It is fundamental to choose the appropriate efficient solutions when deploying data storage systems in data centres.

PrimeEnergyIT through its partner INRIA, has been assessing existing solutions for energy efficient storage systems. At the level of individual components, several technologies have shown promise.

Disk spin-down and variable speed features allow for energy savings in Hard Disk Drives (HDDs) by reducing speed or accessing stand-by mode during periods of inactivity. However the concrete options for savings generally depend on the characteristics of the application workloads. Spinning disks down far too often can degrade performance and reduce the lifetime of drives. Therefore, several algorithms have been developed at the operating system and application level to explore the periods of inactivity. Some solutions attempt to reschedule the data access requests, thereby increasing the length of idle periods, prodiving potential for higher energy savings.

Solid State Drives (SSDs) are another promising technology. In addition to substantially higher performance compared to HDDs when considering application workloads with mostly random data access, SSDs consume much less power than their counterparts due to the lack of moving parts such as motors and actuator heads. Although the price per MB of SSD storage is still higher than for HDDs, the production cost of SSDs has dropped considerably. SSDs provide a good complementary solution, at the individual component level where they are used as large buffers in Hybrid Hard Drives (HHDs) and at the system level where they are employed as level 0-1 high-performance storage.

At the level of complete storage solutions, such as Direct-Attached Storage (DAS) and Network-Attached Storage (NAS), manufacturers offer a large range of products and concepts respectively features and components which can be used to improve energy efficiency. Among others the following components and approaches are used to increase energy efficiency:

Energy efficient power supplies (using certified units [2]).
Use of mixed drives in the same enclosure. By mixing high-performance low capacity drives with low-performance high capacity drives, it is possible to carry out application tiering by moving data to drives that consume less power as the demands for a particular data set become less frequent.
Software systems allowing for seamless and automatic tiering by moving data to the appropriate tier based on ongoing performance monitoring.
Small-Form-Factor (SFFs) enclosures that save floor space in data centres and can increase the energy efficiency by using 2.5-inch HDDs and SSDs.
More energy-efficient RAID levels.
Combination of server virtualisation with storage virtualisation. Consolidating storage in pools and allocating capacity in small increments or via thin provisioning can provide considerable savings as the storage efficiency can be increased to above 70%.
Use of multi-protocol network fabric can reduce floor space and cooling requirements.
Data compression and de-duplication. Compression and de-duplication can reduce the data-footprint and maximise the storage efficiency.

In addition to these solutions, there are a number of technologies and practices to be considered when designing the storage for data centres as for example clear and sound policies for data retainment and backup etc.
The complete report from the technology assessment will be available by end of April 2011.

[1] The Digital Universe Decade - Are you ready? IDC, May, 2010.
[2] 80PLUS Certified power supplies, http://www.80plus.org/.
[3] SNIA Green Storage Initiative, http://www.snia.org/forums/green/