Image: Seagate

SSDs may be a lot faster than HDDs, but they could be the wrong choice for the environmentally conscious.

That’s according to at least two researchers from the University of Wisconsin-Madison and the University of British Columbia, who have shared a new report exposing “the dirty secret of SSDs.” Although SSDs are also favorable for consuming less power than their mechanical counterparts (56.9 kWh for an SSD versus 183.9 kWh for an HDD over five years of use), the researchers came to the conclusion that they do result in significantly higher combined CO2 emissions.

An SSD emits 184 kg. of CO2 over five years, while an HDD with the same capacity emits only 99.6 kg., according to the report. The test involved 100 SSDs and something called a storage embodied factor, per Basic Tutorials, which spotted the research.

To do this, the researchers say they compared 94 LCA reports of SSDs to better understand the carbon footprint. For the comparison, they calculated a so-called storage embodied factor (SEF), which represents the rate of CO2 emissions with the capacity of the storage medium.

On average, SSDs would have a SEF of 0.16, while classic mechanical hard disks would only have a SEF of 0.02.

While most CO2 emissions are generated in the production of SSDs, it is exactly the other way around for HDDs. These are significantly less harmful to the climate in production, but in the long term will require more CO2, they said.

“HDDs are more bulky and require more material in manufacturing,” the researchers said. “Therefore, one might think that manufacturing would require more CO2 emissions compared to SSDs. However, our analysis of 24 published LCA reports shows that exactly the opposite is true.”

The researchers have presented four solutions to compensate for SSDs’ higher emissions. One includes the use of single-level cells (SLC) as opposed to multi-level cells (MLC), the latter of which can be recycled and reused for the former, albeit with lower capacity.

Hard drives remain king in terms of cost/capacity, but they have been completely overshadowed by SSDs in the performance department, particularly following the advent of modern standards that include NVMe.

Source: arXiv (via Basic Tutorials)

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4 comments

  1. Weight/mass of CO2 is extremely misleading. Combustion of carbon combines it with O2 already in the atmosphere. Carbon accounts for 12 atomic mass units of CO2's molecular weight (44). Only 27% of the mass of CO2 emissions is material that wasn't already in the atmosphere.

    So chips on an SSD take more carbon to produce than HD platters. Do they account for transport demands?
  2. I mean.... hard drives are made of f*cking metal man. That sh!t has to be mined, forged, pressed etc. All that involves huge heavy equipment that spews carbon. Then they take more power to spin and operate than SSDs.

    SSDs are just chips, made from silicon / ie - sand. Sure the manufacturing plants don't help but you would have those either way.

    edit - oh ok it references output by capacity, and in that way hdd's do have a massive advantage bc of density. Still... I'm not buying it.
  3. I mean.... hard drives are made of f*cking metal man.
    Most metal is nearly infinitely recyclable. Once it's been extracted and processed initially, it has a fairly low carbon intensity. Silicon, on the other hand, is notoriously difficult to recycle and is extremely energy and carbon intensive in manufacture. You can't just take the same lump of silicon and recycle it back into a new lump of newer silicon -- at least in the same way you can aluminum housings and glass platters.

    That said, I agree with your general premise. I don't buy that HDDs are better enviromentally.

    I grant you, the manufacturing angle of that is ~probably~ minor. SSDs don't use a massive amount of silicon in the first place.

    The power is a real concern - a drive that's on 24x7, efficiency really starts to add up. You have a lot of factors there - HDDs don't vary too much with load (the platters always spin, the drive arm doesn't take a lot of power), but SSDs do take a hit under load. SSDs can idle in the milliwatts, but HDDs have to keep that platter spinning -- once you get it up inertia helps, but you are still in the watts, not milliwatts. Now, HDDs can "sleep" and spin down, but they incur a massive seek penalty to spin back up, and a big power hit to get the platters back up to speed. SSDs win the power part hands down, but the amount they win by varies widely based on the work load and how much you can let the devices idle versus sleep.

    And yeah, once you bring capacity into the equation, then the massive density of the latest hard drives will crush SSDs, if you are looking at Watts per Byte Stored. I don't think you can look at it that way, you really need to look at watts per byte transferred (either read or write) - because you get constrained by the transfer speed of the interface. The storage density itself is irrelevant really, unless you are just looking at the cost to park data and have it available - not actually access it. Which isn't really a good metric, because that doesn't do anyone any good and you could get something like tape or iced storage to look like a freakin' rock star -- zero energy requirement past the initial write and huge density on what amounts to just plastic film (or glass optical media, if you really wanted to get environmental about it). Once you take the fact that HDDS transfer slower, and their density doesn't really do them any good ... yeah, I don't know how those numbers would look exactly, but I suspect SSDs would win out on that -- vastly faster with generally lower power requirements.

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