On Monday, memory and storage vendor Micron announced that its new 176-layer 3D NAND (the storage medium underlying most SSDs) process is in production and has begun shipping to customers. The new technology should offer higher storage densities and write endurance, better performance, and lower costs.
The new NAND process is Micron's fifth generation of NAND and its second generation of replacement-gate architecture—a replacement to the earlier, floating-gate architecture used by both Micron and Intel in the past. In traditional floating gates, insulators separate individual cells, which results in undesired capacitance between cells.
Micron's replacement-gate architecture instead builds multiple cells into a single insulating structure, virtually eliminating cell-to-cell capacitance, and (according to Micron) increasing write endurance, power efficiency, and performance. The company has not yet provided concrete benchmarks quantifying these claims.
Increased layer count
The new 3D NAND process builds more cell layers into each chip, offering greater storage density, lower access latencies, and better power efficiency. For reference, Micron's current floating-gate NAND offers 96 layers, its previous generation of replacement-gate NAND offered 128, and Western Digital's BiCS5 3D NAND process offers 112 layers.
Increasing layer count means significantly decreasing die size at the same number of storage cells. Micron claims the new chips feature 30-percent reduced die size over best-in-class competitive offerings. This makes higher storage capacity more practical in smaller form factors.
We should be clear, the practicality of increased storage in smaller form factors here means very small form factors, such as M.2 NVME drives and integrated eMMC storage. Although consumers are accustomed to higher capacity in conventional disks than in SSDs, the limitation is cost, not volume. Storage vendor Nimbus began selling a 100TB SSD in the traditional 3.5-inch hard drive form factor more than two years ago; meanwhile, Western Digital only began selling 20TB conventional hard drives this July.
In addition to the increased areal density, Micron says the new process offers significant improvements in both read and write latency—a 35-percent improvement compared to its current floating-gate NAND and a 25-percent improvement over its first-generation replacement-gate NAND.
The biggest performance takeaways here aren't to be found in the typical selection of overwhelmingly large numbers favored by marketing departments—that is, the absolute top speed a drive can achieve for extremely large operations under ideal conditions. More importantly, they mean improved Quality of Service (QoS)—in other words, more consistent speeds, even under less than ideal workloads and conditions.
Micron's newly improved latencies should also mean better performance on the low end—in other words, 4KiB or smaller blocksize operations, which aren't being conducted in massively parallel workloads.
What this could mean for consumers and enterprise
If Micron's claims of greatly increased write endurance pan out, it might become possible to replace incredibly expensive SLC (Single Layer Cell) enterprise/data center SSDs with much cheaper 3D NAND devices in demanding applications. Meanwhile—assuming no large increase in per-wafer manufacturing cost—the roughly one-third increase in storage density per chip could mean similarly less expensive consumer devices.
We don't expect this to be the death knell for traditional hard drives yet. Even in the best possible case—no increase in manufacturing cost whatsoever—this would put the cost per terabyte of TLC NAND somewhere around $85. The cost per TB of conventional hard drives runs about $27, so there's still plenty of air between the two technologies when it comes to price.