Realisation of a Sustainable Future in Data Storage

Author : Rainer Kaese, Toshiba

26 September 2023

Figure 1: HDDs are 7x cheaper in terms of $/GByte
Figure 1: HDDs are 7x cheaper in terms of $/GByte

The storing of large quantities of data is essential to so many aspects of our modern world, as is protecting the environment. Yet, these 2 needs often seem to be ‘at odds’ - with the majority of cloud data being held on hard disk drives (HDDs) that many consider to be power hungry.

The following article looks at how advancements in HDD technology are helping to dramatically reduce the power consumed for storage purposes and consider other ways that HDDs can help us comply with our environmental goals.

Why use HDDs for the cloud?
Data is valuable these days, so storage and retention is an important consideration for this 21st Century ‘currency’. The 3 primary options for storage are tape, HDDs and solid state drives (SSDs) - each of which has its own distinct attributes.

Tape is primarily a backup media. It is very reliable and low cost, but access is far too slow for it to be considered as a cloud storage medium. This leaves HDDs and SSDs, both of which are viable considerations for cloud storage from a performance perspective.

While there are differences in power consumption and speed (SSD is faster and lower power), the biggest gap between the 2 technologies is cost.

When we look at the cost per unit storage, we first notice that the bit cost of HDDs is 1/7th that of SSDs. Equally interesting is that both costs are continuing to fall at a similar rate so, based on current projections, there is no expectation that SSD will become lower cost than HDD in the short-to-medium term.

With the scale of cloud storage, cost is a primary consideration and, for this reason, the vast majority of cloud storage is based on HDDs. As a direct comparison1, there were 88 million 3.5” / 7,200rpm Enterprise-HDDs shipped in 2022 (a total of 1021 Exabytes) while 66 million Enterprise-SSDs shipped for a total capacity of just 175 Exabytes.

HDD power consumption reduces through innovation
Given the scale of cloud storage, the energy consumption of HDDs is a significant consideration. The industry thinks in terms of W/TByte - as this is a good measure of how much energy is needed globally to store all of the data in the cloud. 

Figure 2: W/TByte figures have dropped 5-fold in a decade
Figure 2: W/TByte figures have dropped 5-fold in a decade

This measure also reflects the fact that to spin platters will always take a finite amount of energy, which is an unavoidable attribute of HDDs. So, while the industry continues to seek efficiencies in power consumed, in parallel they are increasing HDD capacity while ensuring power consumed does not rise.

Back in 2011, a 4TB HDD (MG03 series) consumed around 10.5W - considered ‘state-of-the-art’ at that time. That equated to a 2.6W/TB consumption figure. By 2017 the capacity had increased 2.5x, while innovations had meant that power consumption remained almost constant (10.6W). Consequently, the W/TByte had more than halved.

It was at this time, facing a need to use thinner platters to increase capacity, the air that filled the drives started to cause challenges with ‘fluttering’ during rotation. By replacing air with helium, this issue was overcome - as it is a thinner gas that causes less friction on the platters. This is reflected in a 2.8W reduction in the overall HDD power consumption, as the motor has to work less hard.

So, through capacity increases, incorporation of helium and other innovations, the W/TByte of a typical enterprise HDD has dropped 5-fold from 2.6W/TByte to 0.5W/TByte, which will significantly impact the energy needed to power cloud storage. The 2022 release of the 20TByte MG10ACA continued the improvement with an extra 2TBytes of capacity, although active power only increased by 1W.

How use cases impact power consumption
Inherent within HDDs are further power-saving opportunities through the incorporation of idle and standby modes. If we consider an 18TByte MG09 HDD, the operating power is around 8.3W when the platters are spinning, and the heads are moving to randomly read and write data. However, there are 3 ‘idle’ modes and a standby mode.

Figure 3: Idle modes offer opportunities for future power saving

In standby mode, the power consumed reduces to 0.43W, but this involves stopping the platters from rotating. While this is attractive from a consumption perspective, it can take up to 20s to spin the platters and be able to read/write data. Clearly, this is not viable for online storage.
The idle modes variously switch off parts of the magnetics and/or electronics while the spindle continues to rotate. In these modes, the ‘wake up’ time is between 1.2s and 0.3s. However, with storage schemes such as RAID and SDS, there is frequent access even when the drive appears to be idle. This, therefore, precludes the use of these idle modes for power saving for now.

Upgrade to improve
As HDD reliability is strong, failure rates have dropped significantly. Therefore, since 2010, there has been a huge installed base of HDDs with SATA 6GBytes/s interfacing featured. However, as these are reliant on older technology, their W/TByte figures are significantly higher than modern higher capacity HDDs.

As the interface and form-factor is identical, it is a relatively easy exercise to simply swap the older drives for newer versions. In doing so, data centre operators will benefit from more storage in the same space and power consumption will, at worst, remain the same. If moving to helium-filled HDDs, then the benefit will be greater - as a up to 30% power saving can be anticipated.

HDD life cycle
One of the most sustainable ways to use HDDs is to run them for longer - 5 years or even more. This is much more possible now, as annual failure rates (AFRs) have dropped by 50% (0.73% to 0.35%) in the past decade. 

Figure 4: Higher reliability (MTTF) leading to lower AFRs.

Considering sustainability, we must remember that every HDD is comprised of up to 1kg of metal and other components/materials. This is a valuable resource of aluminium and copper that can be shredded and recycled when the HDD reaches end of life. In future, as resources become more scarce, removing and re-using the rare-earth magnets is a potential sustainability win.

Emerging technology
The latest HDDs from Toshiba are the MG10ACA series, which are available with 12Gbit/s SAS or 6Gbit/s SATA interfacing. These 3.5” units incorporate multiple shock and rotational vibration (RV) sensors for use in multi-bay systems. 10-platter and microwave assisted magnetic recording (MAMR) technologies increase the storage density to 20TBytes. The HDDs in this series offer a reliability of 2.5 million hours MTTF equal to an AFR of 0.35% within a warranty time of 5 years at a rated workload of 550TBytes/year.

Summary
HDDs are by far the best storage technology choice, primarily due to their low cost and high capacity. However, with their large-scale deployment, the industry is paying attention to their power consumption and sustainable use.

Innovation has allowed the W/TByte figures to fall 5-fold in a decade and the introduction of helium in 2017 has dropped power consumption by 30%. In the future, adapting RAID and SDS storage schemes may allow the use of idle modes (which exist today) to achieve further dramatic reductions.

Modern HDDs last longer and consume similar power levels to earlier generations. This allows them, and the associated power supplies, to be used for longer - often more than 5 years.


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