Final Thoughts
Several exciting changes will affect the client storage market this year. SSDs are on track to receive a higher-performance interface and simplified set of commands. At the same time, flash is growing up (literally). These advancements will divide the market. While lower-cost products rival mechanical storage on the value front, high-performance products will allow new applications to thrive.
The two buzzwords for 2015 are Non-Volatile Memory Express (NVMe) and 256-bit 3D NAND. NVMe is a set of commands that unbinds NAND from the limitations of the Advanced Host Controller Interface. AHCI was introduced as the register-level interface for SATA. When SATA was introduced, flash in the densities we have today wasn't on the horizon. Back then, hard drives were going to rule for decades. Of course, their mechanical nature capped performance, limiting the utility of deep queue depths. SATA capped native command queuing at 32 queues of one command (far more than was needed). NVMe increases this limit to 64,000 queues, and each queue can sustain up to 64,000 commands.
NAND flash is advancing, too. Improvements in manufacturing technology already enabled the first 3D V-NAND from Samsung. IMFT will follow with 3D flash by mid-2015, and it's rumored that we'll see 256Gb densities. Overnight, 1TB SSDs will turn into 2TB SSDs. The manufacturing costs should be equal once the dust settles, so your wallet won't suffer when it comes time to step up capacity.
Also on the flash front, expect more three-bit-per-cell flash, also referred to as TLC. Many of the charts in this editorial show an unbranded SSD under the SMI SM2256 name. This is a R&D board from Silicon Motion with a new controller that should hit the market in a few months. It's designed to support cheap TLC flash with P/E cycles as low as 500. Advanced LDPC algorithms are expected to extend low-cost flash life to the levels we enjoy today. So, by the end of 2015, 256GB SSDs may sell for as little as $50.
The new high-performance products will definitely require some tweaking to our test methods. But the low-cost stuff probably will as well. Faster storage is expected to hit ceilings limited by its host interface, PCI Express. Currently, that means a four-lane PCIe 3.0 link, or 32Gb/s. PCIe 4.0 isn't too far off either. LDPC will adapt to changing flash as the medium wears. If an error occurs, the controller goes back to reread the flash cells. This will increase latency.
We are already seeing the effects of low-cost TLC flash causing issues with performance loss in Samsung's 840 EVO. That drive's 1xnm NAND shows signs of read retries after just a few months of data at rest. If Samsung shuffles the information too often, the product won't satisfy its minimum warranty standards. It's a tough position to be in for the best-selling consumer SSD of all time. In the coming months, we'll roll out a new test for the condition in question. And because this is a living document, we'll fill you in first.
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Chris Ramseyer is a Contributing Editor at Tom's Hardware, covering Storage. Follow him on Twitter @chrisramseyer and on Facebook. Follow us @tomshardware, on Facebook and on Google+.
