Considering overheating issues and the reality that raw bandwidth only goes so far, suffice it to say that the latest generation of PCIe Gen 5 SSDs didn’t exactly surprise us. So what to make of the news that SSD controller specialist SiliconMotion is already deep into Gen 6 technology?
In the post regarding Chinese flash market (By Tom’s equipment) SiliconMotion CEO Wallace C. Kou revealed that the company’s first PCIe Gen 6 controller chip, dubbed the SM8466, is “in development.”
Kou did not provide any specifications, although he did say that the chip is manufactured on a 4nm process. This is likely the TSMC N4 and a clear improvement over the N6 node used by today’s most advanced SiliconMotion controllers.
This is significant because one of the hallmarks of the initial series of PCIe Gen 5 SSDs was excessive power consumption and overheating, likely in part due to the employ of an archaic silicon node.
Admittedly, it was a Phison E26 chip built on older 12nm silicon. SiliconMotion’s own Gen 5 controller, the SM2508, has actually been delayed to allow for the jump to the 6nm node and hopefully bypass these issues.
So it stands to reason that if 6nm is required for Gen 5 to function properly, then 4nm would be a good idea for the even more demanding Gen 6 protocol.
Speaking of which, PCIe Gen 6 theoretically doubles the bandwidth compared to Gen 5. This means that the peak bandwidth for a four-lane drive is 32 GB/s compared to 16 GB/s for Gen 5.
Of course, in practice there are various limitations. For starters, there are protocol overheads that limit the effective data rate. Then there are hardware limitations in the form of NAND and controller chips, and even broader signal integrity.
For example, the SiliconMotion SM2508 controller has a peak speed of 14.5 GB/s and 14 GB/s sequential read and write, not the full 16 GB/s. Therefore, it is secure to say that the modern SM8466 will not reach 32 GB/s.
More specifically, it’s highly unlikely that there will be any NAND flash chips capable of delivering the full 32GB/s of bandwidth once the first Gen 6 drives arrive. Another issue is that peak throughput isn’t everything.
Latency and random access to 4K resolution are also very critical. The SM2508 has a performance of 2.5 million IOPS in both directions, and it will be very captivating to see how much progress the modern Gen 6 chip offers.
Ultimately, latency is not something that NAND flash technology does very well, especially compared to, say, RAM. Intel’s 3D XPoint solution, also known as Optane, was much better in this regard, but it failed and was discontinued.
All of this means that we’re not necessarily very excited about the prospect of Gen 6 drives. They’ll definitely be faster in terms of maximum throughput. But will they make our computers run faster and our games load faster? This is all much more questionable.
Either way, given that the modern Gen 6 controller is still in development and we haven’t actually gotten our hands on an SSD with a SiliconMotion Gen 5 chip yet, it’s secure to say that it’ll still be a while before we get anywhere near what’s possible purchase Gen 6 drive powered by SiliconMotion.
