Testing SATA Express And Why We Need Faster SSDs

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.