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
POST A COMMENT

131 Comments

View All Comments

  • SirKnobsworth - Thursday, March 13, 2014 - link

    Thunderbolt 2 is really PCIe x4 + DisplayPort in disguise, and you don't need DisplayPort to your SSD. Reply
  • MrSpadge - Thursday, March 13, 2014 - link

    Couldn't you build a nice M.2 to SATAe adapter in a 2.5" form factor and thereby reuse your existing M.2 designs for SATAe? Reply
  • Kristian Vättö - Thursday, March 13, 2014 - link

    Technically yes, but the problem is that M.2 is shaped differently. You could certainly fit a small M.2 drive with only few NAND packages in there but the longer, faster ones don't really fit inside 2.5". Reply
  • Kevin G - Thursday, March 13, 2014 - link

    "At 24 frames per second, uncompressed 4K video (3840x2160, 12-bit RGB color) requires about 450MB/s of bandwidth, which is still (barely) within the limits of SATA 6Gbps."

    This is incorrect:

    3840 * 2160 * 12 bit per channel * 3 channels / 8 bits per byte * 24 fps ~ 896 MByte/s

    And that figure is with with good byte packing. For raw recording, the algorithm may pack the 12 bits into two bytes for speed purposes meaning you'd need about 1.2 Gbyte/s of bandwidth. Jumping to 4096 x 2160 resolution at 12 bit color and 30 fps, the bandwidth need grows to about 1.6 Gbyte/s.

    The other thing worth noting is that uncompressed recording is going to take a lot of storage. A modern phone recording at the highest quality settings with 64 GB of storage would last less than 40 seconds before running out.
    Reply
  • Kristian Vättö - Thursday, March 13, 2014 - link

    Oh, you're absolutely right. I used the below calculator to calculate the bandwidth but accidentally left "interlaced" box ticked, which screwed up the results. Thanks for the heads up, fixing... Reply
  • Kristian Vättö - Thursday, March 13, 2014 - link

    And the calculator... http://web.forret.com/tools/video_fps.asp?width=38... Reply
  • JarredWalton - Thursday, March 13, 2014 - link

    Aren't there *four* channels, though? RGB and Alpha? Or is Alpha not used with 12-bit? Reply
  • Kevin G - Thursday, March 13, 2014 - link

    No real way to record with an Alpha channel value to my knowledge. Cameras and scanners etc all presume a flattened image as if everything were solid. The only exception to this would be direct frame buffer capture from video memory which can independently process an Alpha channel.

    Input media would generally be 36 bit. During the editing phase an Alpha channel can be added as part of compositing pipeline bringing the total bit depth to 48 bit. Final rendering can be done to a 48 bit RGBA file. Display output on screen will be reduced to 36 bit due to compositing for the frame buffer.
    Reply
  • Nightraptor - Thursday, March 13, 2014 - link

    When I saw the daughterboard Asus provided my instant thought was actually using this (in pcie 3.0 form) to somehow provide the option to add an external GPU to a tablet. I may be the outlier, but my dream would be to have and 11.6" 16:10 1920 x 1200 tablet with the ability to connect a keyboard dock to function as a laptop, or another dock with a discrete graphics card to function as a desktop for occasional gaming (1080p at high setting would be all I'd ask for - so pcie 3.0 4x should be sufficient). If you could somehow get a SATAe cable on a tablet I think this would do it. Reply
  • vladman - Thursday, March 13, 2014 - link

    If you want speed from storage, get a nice Areca PCIe RAID controller, attach 4 or more fast SSDs, do RAID 0, and you've got anywhere from 1.7 to 2GB/s of data transfer. Done deal. Reply

Log in

Don't have an account? Sign up now