SSDs gear up for five-fold speed boost

A host interface developed specifically for solid-state storage, NVMe is about to break the SATA bottleneck


We’ve come a long way from the model of a single PC per household. The new norm is multiple smart devices per user, most of them connected to the cloud. These devices, which will number in the tens of billions by 2020, according to Cisco -- are continuously generating content for data centers to process, from users chatting on social networks, to video feeds between their mobile devices. This insatiable desire for ever faster access to high-quality information might be the death knell for hard disk drives.

If we look at networking speeds available for PCs, wireless connectivity has evolved from 802.11n at 600Mbps to 802.11ac at 1,300Mbps. Intel’s sixth-generation Core PC platform, also known as “Skylake,” introduced 802.11ad (Wi-Gig) that can operate at 7,000Mbps. Wired speeds have also evolved -- from USB 2.0 at 480Mbps to new PCs with USB 3.1 at 10,000Mbps and Thunderbolt 3 at 40,000Mbps.

However, the benefits of the new networks will not be realized unless a system is well-balanced. Up until the last generation of PCs, local storage has not been a bottleneck to information flow from the device. Hard disk drives can support approximately 125MB per second (1,000Mbps) of throughput, which until now has been sufficient to keep up with PC networking speeds. However, with the new platforms, 125MB per second is woefully inadequate. For the first time in history, HDDs have become the bottleneck for data flow out of a PC (see figure below).

Solid-state drives, which use NAND flash memory instead of spinning disks, can easily alleviate the performance gap. SATA SSDs typically have speeds of about 550MB per second (4,400Mbps). However, even these drives cannot keep up with the latest generation of networking speeds. 

networking storage speeds

PC networking vs. storage speeds

Dawn of a new era

The limitation with SATA SSDs is not its use of NAND flash memory, but the host interface itself. SATA was originally designed for slower storage media like HDDs. While the interface has evolved to 6,000Mbps, it has hit its limit in terms of speed bumps. To truly unleash the power of flash, an interface designed from the ground up is necessary. And now it’s here. 

The industry has standardized on a protocol called NVMe (Non-Volatile Memory Express) that communicates over the PCIe host interface. This standardization paves the way for mass adoption of NVMe technology, which means low cost for consumers. The interface scales up by using multiple lanes. An NVMe SSD using four lanes has a speed of 32,000Mbps, which is more than five times faster than SATA SSDs. 

Bandwidth is not the only difference between SATA and NVMe. Because NVMe was developed for faster, solid-state storage, more parallelism has been designed in -- much more. SATA supports a single queue that can hold up to 32 commands. In contrast, NVMe supports 64,000 queues that can each hold up to 64,000 commands. 

Imagine yourself checking out groceries at the store. SATA, with its single queue, would be like having a single checkout line. NVMe, on the other hand, is like having multiple checkout lines operating in parallel. If you have a quad-core computer running SATA, all of the commands need to funnel through a single core to be completed. With NVMe, command completions are done in parallel across all four cores. This parallelism, along with a more efficient protocol, increases throughput and reduces latency.

Impacts of NVMe

NVMe SSDs will unleash the blazing performance of flash to increase productivity. Imagine you went to a conference and received lots of great material -- 10GB worth of PowerPoint presentations and articles. With a SATA HDD, sharing this material through your computer with another colleague via a USB 2.0 stick would take at least six minutes. With NVMe and a Thunderbolt 3 connection, it would take less than 10 seconds. 

This faster time to complete tasks also extends a laptop’s battery life. There is a very large difference between active and idle power in a storage device. Let’s take the previous example of transferring files. The HDD will be at active power of 6W for 180 seconds (three minutes per laptop) to complete the transfer. An NVMe SSD, on the other hand, can complete the same task in 10 seconds. This means 6W of active power for 10 seconds, then using only idle power at 50mW. This translates to 94 percent less power used.

NVMe SSDs reduce the amount of equipment needed in data centers to perform computations. For example, the densest 1U server can accommodate a maximum of 10 2.5-inch drives. Consider that 10 SATA SSDs can provide a combined throughput of 40Gbps (500MB per second per SSD). For the same workload, those 10 drives could be replaced by a single NVMe SSD. This reduction in space, power, and complexity results in significant cost savings, which are ultimately passed down to the consumer.

Let’s take a familiar service as an example: video streaming. It takes 6Mbps to support a 1080p HD video stream. A 1U server with 10 SATA SSDs can support between 6,000 and 7,000 subscribers watching HD. An Ultra HD stream requires about 20Mbps bandwidth, which is about three times the bandwidth of HD. To support the same number of subscribers watching Ultra HD, a provider would need to have three fully equipped servers, along with the associated networking gear, rack space, and power -- all of which will lead to an unacceptable rise in subscription costs. Alternatively, those same requirements can be met with a mere three NVMe SSDs in a single server, alleviating pressure on the service provider to increase rates.

NVMe SSDs will make personal computers more responsive, reduce storage footprints in the data center, and lower power requirements for both clients and servers. It makes no sense to have incredible networking speeds if your storage cannot keep up. Beginning in early 2016, NVMe SSDs will be a necessity for a well-balanced computer system.

Tien Shiah is a product marketing manager for SSDs at Samsung Semiconductor. He serves as a product consultant and market expert, focused on the accelerating migration to SSDs in the client and enterprise marketplaces. He has an MBA from McGill University, a BSEE from the University of British Columbia, and more than 15 years of product marketing experience in the semiconductor and storage industries.

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