Using 176-Layer NAND for High-Capacity Data Center SSDs

Chart with a line that goes pretty flat from 1.5 to 2ms latency 0 to 350K IOPSMicron recently briefed The SSD Guy on its new 7450 SSD series, a range of high-capacity data center SSDs offered in an impressive number of capacities and form factors spanning M.2, U.3 and E1.S. The 7450 is a mainstream drive targeted at a wide variety of data center applications, including common, mixed, and random workloads.

The 7450 series is an evolution of Micron’s 7400 series which was first introduced at 96 layers and was based on a proprietary Micron controller SoC. The 7450 is the 176-layer upgrade.

One of the line’s features that should be most important to enterprise and cloud users is the SSD’s consistently low latency. Micron tells us that the 7450 series has a latency of 2ms to six nines (99.9999%) consistency in a 70/30 Read/Write workload. (Click on this post’s graphic to see how that looks.) The SSD Guy likes to translate the six nines statistic to something that I find easier to wrap my head around. There is only a one-in-a-million likelihood that a latency greater than 2ms will occur.

According to Micron, the SSD’s speed is partly due to a new NAND chip technology called Independent Word Line, which adds parallelism to improve performance and latency. A lot of credit goes into the company’s controller, though. Integrated with Micron’s own DRAM, internally developed SoC and custom-crafted firmware, this vertically integrated SSD was designed with low latency in mind. Micron boasts that this is the first vertically integrated data center SSD made from 176-layer flash.

Big Capacity in Small Packages

Like Micron’s 2TB 2400 SSD shown in an earlier SSD Guy post, this SSD takes advantage of the company’s 176-layer 3D NAND flash. This allows the company to pack more gigabytes onto fewer chips, and that, in turn, supports higher capacity SSDs. Unlike the 2400 client drive, which uses QLC, the 7450 uses TLC NAND. This is more interesting to most data center users since they are using it in compute systems which require very high constant performance under 24:7 utilization versus the more bursty usage and less intensive write environment in client PCs.

Another capacity-boosting chip attribute is CMOS under-the-array (CUA) technology, which tucks the chip’s peripheral logic under the memory array. This allows about 30% more bits to be put onto a chip than the more evolutionary technique of putting the peripheral logic beside the array. An added benefit is that CUA also helps to accelerate the chip’s performance.

By using this 176-layer CuA TLC NAND, Micron was able to squeeze 8 terabytes into an E1.S form factor, and 15.36TB into the U.3 form factor.

Micron has been launching SSDs in a broad range of form factors lately, including legacy M.2 and 2.5” form factors commonly in use today and the new flash-optimized Enterprise Data Center SSD Form Factor (EDSFF). EDSFF provides the signal integrity and improved cooling capability required to maximize performance in future generations of PCIe-based SSDs. The company stressed that the enterprise SATA market is still very healthy, so Micron will continue to support SATA data center SSDs.  Still, the SATA interface is considerably slower than NVMe, so these new PCIe Gen4 drives support I/O 12 times faster than SATA.

Data Protection

These SSDs are aimed at corporate and data center applications, so data security is extremely important. Micron’s approach to that is to enhance the technology underpinning Opal 2.0 self-encryption by outfitting the 7450 with the company’s Secure Execution Environment (SEE) technology. SEE further improves the security of data at rest by physically isolating the hardware used to provide data security, including dedicated secure memory and a dedicated security processing engine. The Micron 7450 SSD series is also optionally able to support Microsoft’s eDrive security protocol.

The M.2 form factor is still widely used in the cloud, so Micron offers Power Loss Protection (PLP) even in a 22×80 M.2 form factor. The company claims to be the only one to offer PLP in this format.

The company’s recent introductions make it clear that Micron plans to use its groundbreaking NAND flash technology to increase its presence in both the data center and the client SSD spaces. It should be interesting to watch this business develop.

(Micron is a client of Objective Analysis.)

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