Are SSDs Really More Sustainable Than HDDs?

Are SSDs Really More Sustainable Than HDDs?

The News: Solid state storage devices are commonly accepted as being more energy efficient than spinning disk alternatives. A research study evaluating the carbon output of storage devices, however, found that the carbon output of manufacturing SSDs is far greater than that of manufacturing HDDs. This challenges the typical thinking around storage device sustainability, and requires additional evaluation. Read the full research paper – The Dirty Secret of SSDs: Embodied Carbon here.

Are SSDs Really More Sustainable Than HDDs?

Analyst Take: Sustainability in IT has become a major talking point with growing concerns over environmental impact and ESG initiatives, and naturally energy efficiency has been at the center of the discussion. When considering data storage, this energy efficiency argument is often discussed with regard to storage devices. The common thought is that SSDs are generally more sustainable than HDDs because they are more power efficient, primarily due to the lack of moving parts. This energy efficiency argument is heavily used in vendor marketing, specifically from storage vendors selling all-flash storage systems.

While energy efficiency is an important factor in evaluating the carbon output and sustainability of a device, it is not fully representative of the lifetime environmental impact. Another key area when considering the carbon output associated with storage devices is the output resulting from manufacturing, also referred to as embodied carbon. A research paper from Swamit Tannu from The University of Wisconsin-Madison and Prashant J Nair from The University of British Columbia titled The Dirty Secret of SSDs: Embodied Carbon discusses the difference in carbon output from manufacturing SSDs and HDDs. The report finds that the carbon output of manufacturing SSDs is much higher than that of HDDs, and in fact it states that SSDs can have an embodied carbon cost around eight times higher than HDDs of the same capacity.

The significant difference in embodied carbon challenges the idea that SSDs are the more sustainable option simply because of energy efficiency. While the report does acknowledge that SSDs contribute significantly less emissions while in use due to energy efficiency, it suggests that this difference might not overcome the environmental cost of manufacturing when evaluating the emissions over the total lifespan. The paper shows a comparison of SSD and HDD emissions over both 5 and 10 years, evaluating the OPEX (emissions attributed to using the device) and CAPEX (embodied emissions). Interestingly, the HDD is shown to have less total CO2e emissions over both time frames.

Image Source: Tannu and Nair

This is a fairly surprising result. The vast majority of vendors claim that SSDs are far more sustainable than HDDs, yet this report seems to show otherwise. So, are SSDs actually less environmentally friendly than HDDs? Well, in practice, the two technologies may have more similar emissions than either the calculation in this report or storage vendors would lead you to believe.

Since the emissions of SSDs are heavily weighted by their embodied carbon while HDDs are more costly in OPEX emissions, the refresh cycles of the devices must be considered to really determine which device is more sustainable over its lifetime. While Tannu and Nair found the HDD to have far less emissions over both the 5-year and 10-year spans, this result is heavily impacted by an assumption that both technologies are on a 5-year refresh cycle. In the above calculations, both the HDD and SSD are replaced after 5 years, doubling the CAPEX or embodied cost.

In practice, however, the technology refresh cycles of HDDs and SSDs have grown apart. A 4- or 5-year refresh cycle, such as used in the previous calculation, is what is typically used for HDDs. SSDs, on the other hand, are not necessarily refreshed as often. Vendor warranties on SSDs have extended up to 10 years in some cases. These longer warranties, combined with the popularity of controller refresh programs that separate the refresh cycles of controllers and storage devices, are allowing IT organizations to keep SSD devices for up to 10 years. Adjusting the Tannu and Nair calculations to a single CAPEX cost for SSDs over a 10-year period would give the SSD a total of 209.2 Kg CO2e. This is still more than the 199 Kg CO2e calculated for the HDD, but much closer than the original 369.2 Kg figure.

It should also be considered that SSD devices are quickly growing in density. QLC devices, such as the 75 TB device recently announced by Pure Storage, are providing much greater density than HDD devices. This difference in density may allow IT organizations to reduce their overall physical footprint, and therefore total emissions. While not an exact calculation, it is likely that a reduction in physical systems, that each require their own manufacturing and power, due to the use of denser storage devices, would make up for the difference between HDD and SSD emissions.

Still, the difference in the sustainability of SSDs and HDDs is likely much closer than many flash storage vendors would like to admit. When considering sustainability, it is important for IT organizations to be aware that there are several influencing factors. The manufacturing of devices may have a large impact, and should not be ignored. The impact of technology refresh cycles will also make a significant difference, and further supports strategies such as utilizing controller refresh programs to break the relationship between refreshing controllers and storage devices. Denser devices that provide significant footprint consolidation may also improve the total carbon emissions in the data center.

Disclosure: The Futurum Group is a research and advisory firm that engages or has engaged in research, analysis, and advisory services with many technology companies, including those mentioned in this article. The author does not hold any equity positions with any company mentioned in this article.

Analysis and opinions expressed herein are specific to the analyst individually and data and other information that might have been provided for validation, not those of The Futurum Group as a whole.

Other insights from The Futurum Group:

Sustainability in IT – A Q3 Reflection

Pure Storage Adds New File Services to FlashArray

The Environmental Impact of Accelerators

Author Information

Mitch comes to The Futurum Group through the acquisition of the Evaluator Group and is focused on the fast-paced and rapidly evolving areas of cloud computing and data storage. Mitch joined Evaluator Group in 2019 as a Research Associate covering numerous storage technologies and emerging IT trends.

With a passion for all things tech, Mitch brings deep technical knowledge and insight to The Futurum Group’s research by highlighting the latest in data center and information management solutions. Mitch’s coverage has spanned topics including primary and secondary storage, private and public clouds, networking fabrics, and more. With ever changing data technologies and rapidly emerging trends in today’s digital world, Mitch provides valuable insights into the IT landscape for enterprises, IT professionals, and technology enthusiasts alike.


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