Why Do We Need Faster SSDs

The claim I've often seen around the Internet is that today's SSDs are already "fast enough" and that there is no point in faster SSDs unless you're an enthusiast or professional with a desire for maximum IO performance. There is some truth to that claim but the big picture is much broader than that.

It's true that going from a SATA SSD to a PCIe SSD likely won't bring you the same "wow" factor as going from a hard drive to an SSD did, and for an average user there may not be any noticeable difference at all. However, when you put it that way, does a faster CPU or GPU bring you any noticeable increase in performance unless you have a usage model that specifically benefits from them? No. But what happens if the faster component doesn't consume any more power than the slower one? You gain battery life!

If you go back in time and think of all the innovations and improvements we've seen over the years, there is one essential part that is conspicuously absent—the battery. Compared to other components there haven't been any major improvements to the battery technology and as a result companies have had to rely on improving other components to increase battery life. If you look at Intel's strategy for its CPUs in the past few years, you'll notice that mobile and power saving have been the center of attention. It's not the increase in battery capacity that has brought us things like 12-hour battery life in 13" MacBook Air but the more efficient chip architectures that can provide more performance while not consuming any more power. The term often used here is "race to idle" because ultimately a faster chip will complete a task faster and can hence spend more time idling, which reduces the overall power consumption.

SSDs are no exception to the rule here. A faster SSD will complete IO requests faster and will thus consume less power in total because it will be idling more (assuming similar power consumptions at idle and under load). If the interface is the bottleneck, there will be cases when the drive could complete tasks faster if the interface was up for that. This is where we need PCIe.

To demonstrate the importance of an SSD from the battery life perspective, let's look at a scenario with a hypothetical laptop. Let's assume our hypothetical laptop has a 50Wh battery and only has two power states: light and heavy use. While in light use, the SSD in our laptop consumes 1W and 3W under heavier load. The other components consume the rest of the power and to keep things simple let's assume their power consumptions are constants and do not depend on the SSD.
 
Our Hypothetical Laptop
Power Consumption Light Use Heavy Use
Whole Laptop 7W 20W
SSD 1W 3W

Our hypothetical laptop spends 80% of its time in light use and 20% of the time under heavier load. With such characteristics, the average power consumption comes in at 9.6W and with a 50Wh battery we should get a battery life of around 5.2 hours. The scenario here is something you could expect from an ultraportable like the 2013 13" MacBook Air because it has a 54Wh battery, consumes around 6-7W while idling and manages 5.5 hours in our Heavy Workload battery life test.

Now the SSD part. In our scenario above, the average power consumption of our SSD was 1.4W but in this case that was a SATA 6Gbps design. What if we took a PCIe SSD that was 20% faster in light use scenario and 40% in heavy use? Our SSD would spend the saved time idling (with minimal <0.05W power consumption) and the average power consumption of the SSD would drop to 1.1W. That's a 0.3W reduction in the average power consumption of the SSD as well as the system total. In our hypothetical scenario, that would bring a 10-minute increase in battery life.

Sure, ten minutes is just ten minutes but bear in mind that a single component can't do miracles to battery life. It's when all components become a little bit faster and more efficient that we get an extra hour or two of battery life. In a few years you would lose an hour of battery life if the development of one aspect suddenly stopped (i.e. if we got stuck to SATA 6Gbps for eternity), so it's crucial that all aspects are actively developed even though there may not be noticeable improvements immediately. Furthermore, the idea here is to demonstrate what faster SSDs provide in addition to increased performance—in the end the power savings depend on one's usage and in workloads that are more IO intensive the battery life gains can be much more significant than 10 minutes. Ultimately we'll also see even bigger gains once the industry moves from PCIe 2.0 to 3.0 with twice the bandwidth.

4K Video: A Beast That Craves Bandwidth

Above I tried to cover a usage scenario that applies to every mobile user regardless of their workload. However, in the prosumer and professional market segments the need for higher IO performance already exists thanks to 4K video. At 24 frames per second, uncompressed 4K video (3840x2160, 12-bit RGB color) requires about 900MB/s of bandwidth, which is way over the limits of SATA 6Gbps. While working with compressed formats is rather common in 4K due to the storage requirements (an hour of uncompressed 4K video would take 3.22TB), it's not uncommon for professionals to work with multiple video sources simultaneously, which even with compressing can certainly exceed the limits of SATA 6Gbps.

Yes, you could use RAID to at least partially overcome the SATA bottleneck but that add costs (a single PCIe controller is cheaper than two SATA controllers) and especially with RAID 0 the risk of array failure is higher (one disk fails and the whole array is busted). While 4K is not ready for the mainstream yet, it's important that the hardware base be made ready for when the mainstream adoption begins.

What Is SATA Express? NVMe vs AHCI: Another Win for PCIe
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  • MrSpadge - Friday, March 14, 2014 - link

    You're right, the increased interface power consumption won't matter much and will be counterbalanced by the quicker execution time. But as far as I understand the bulk of SSD power draw under load, especially for writes, comes from the actual NAND power draw (unless the controller would be really inefficient). If this is true higher performance automatically equates higher SSD power draw under load. Reply
  • willis936 - Thursday, March 13, 2014 - link

    I love SATAe and NVMe but whenever SAS is mentioned as a comparison it would be nice to use 12G numbers. I noticed a Microsoft graph showed the 6G but didn't even label it. A doubling of bandwidth is nothing to sneeze at. That said SAS is expensive and is for a very different market. Reply
  • Flunk - Thursday, March 13, 2014 - link

    I think they're really making a mistake trying to keep the same connector as SATA. Tacking on a new cable that looks so unwieldy just seems silly. And why not just use M.2 slots? Especially if this is for notebooks (and based on the power usage comparisons it seems like it is, otherwise why would it matter?).

    I suspect this will go nowhere. Reminds me of ISA 2.0.
    Reply
  • Rajinder Gill - Thursday, March 13, 2014 - link

    Backwards compatibility with existing SATA devices was the primary reason for keeping the connector as part of the interface. :) Reply
  • Flunk - Thursday, March 13, 2014 - link

    I understand that, but there isn't much reason not to have 2 sets of ports with the legacy ones slowly disappearing on a desktop. The ports are not large and there is plenty of space. This way we're stuck with a future of badly-designed ports far past the end of SATA's lifetime. Reply
  • Kristian Vättö - Thursday, March 13, 2014 - link

    SATA Express is mainly for desktops -- in mobile M.2 will be the dominant form factor (though SATAe might have some place there too as I mentioned in the article).

    As for power consumption and battery life, that was about PCIe in general.
    Reply
  • phoenix_rizzen - Thursday, March 13, 2014 - link

    So why not add M.2 slots to the desktop, in a vertical orientation, and just make M.2->M.2 cables? Then add the M.2 connector to desktop drives? Reply
  • TheinsanegamerN - Monday, March 24, 2014 - link

    because, silly, that would mean being progressive and eliminating all backwards compatibility, and we CANT do that! /s

    in all seriousness, that would be much nicer. manufacturers would probably throw a temper tantrum, but aside from that, it would be a great solution.
    Reply
  • grahaman27 - Thursday, March 13, 2014 - link

    I would like to see USB 3.1 replace sata6. It sounds unusual, but with the combination of 10Gbps speeds, the new two-way small connector, and integrated power, I think it would really be useful for the expandability and tidiness inside my computer. Reply
  • Veramocor - Thursday, March 13, 2014 - link

    Just posted that later on. I have an external usb 3.0 hardrive why can't I have an internal one. Even better would be thunderbolt 2 at 20 Gbps. Reply

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