Samsung accidentally leaks details of its upcoming 980 Pro NVMe SSD

Enlarge / The 980 Pro offers up to 7,000 MB/sec throughput, on the right workloads—but you'll need a PCIe 4.0 motherboard, a very fast CPU, and good system cooling to take advantage of it.Samsung

Everybody makes mistakes sometimes, and it looks like Samsung made one yesterday: the product page for its upcoming 980 Pro NVMe SSD went briefly online before being discovered by TechPowerUp and then getting yanked offline again.

The 980 Pro is a particularly interesting product, since it shakes up Samsung's lineup in several ways. We've known since CES 2020 that it would be the company's first consumer-available PCIe 4.0 SSD.

The higher-bandwidth PCIe4 bus allows for a blistering throughput increase; the 980 Pro is rated by Samsung for up to 7000MB/sec of throughput, compared to the PCIe3 970 Pro's 3500MB/sec. Unfortunately, the 980 Pro's sharp increase in throughput comes with an equally sharp decrease in warranted write endurance.

980 Pro 970 Pro 970 Evo
Seq Read * Seq Write * Seq Read * Seq Write * Seq Read * Seq Write *
7000 MB/sec 5000 MB/sec 3500 MB/sec 2700 MB/sec 3400 MB/sec 2500 MB/sec
Write Endurance Write Endurance Write Endurance
600 TBW 1200 TBW 600 TBW

You should take these numbers with enormous grains of salt—besides being leaked, they're all filtered through several layers of marketing shenanigans. For one thing, they're in MB/sec, not MiB/sec—so lop 5 percent off the top. For another, they're very deliberately listed in megabytes, not gigabytes, with the same potential confusion between 10^3 and 2^10—so another chunk comes off the top if you're inclined to think of it in GiB/sec.

The 980 Pro's 7000MB/sec really boils down to 6.5GiB/sec… and even that's entirely up for grabs. The fine gray print further down the page says that results "may vary based on system hardware and configuration." That's a meaningful disclaimer—in our experience, NVMe M.2 drives have a distinct tendency to overheat and thermally regulate. You'll also need a mean CPU to keep up with 6.5GiB/sec throughput without bottlenecking.

What we can reasonably expect is significantly increased performance, with—unfortunately—significantly decreased long-term lifespan. To understand why the write endurance—and thus effective lifespan of the drive—dropped so sharply, we'll need to take a peek under the hood.

Understanding NAND terminology

In order to understand the 980 Pro's change in endurance, you need to understand at least a little bit about the NAND flash-storage medium used by most SSDs. NAND flash comes in SLC, MLC, TLC, and QLC varieties—with the leading initial standing for Single, Multi, Tri, and Quad, respectively. Unpacking this a bit further, what we're really talking about is the number of bits stored by each cell.

SLC is the fastest, highest write endurance and most expensive NAND cell type. Each cell only stores a single bit—but this means there are only two meaningful voltage levels per cell to read or write. With charge levels effectively being simply "on" or "off," SLC media can tolerate plenty of sloppiness in both reading and writing of the cells before any errors occur that might require retries or even result in data loss.

MLC media is a misleading term, and Samsung's marketing department leans heavily on that fact in its spec sheets above. Although MLC literally just means "Multi-Level Cell," in common industry use it specifically refers to only two bits per cell. This means each cell must have four distinguishable voltage states, corresponding to numbers 0 through 3. This makes for a cheaper drive at the same capacity, since you only need half the cells a comparable drive made of SLC would—but it's a bit slower to read or write values, and sloppiness in charge state as the drive's write endurance decreases hits you correspondingly faster.

Now that you've got the pattern, TLC means three bits per cell and eight distinguishable voltages corresponding to values 0 through 7. QLC—as seen in Samsung's big, cheap QVO drives—goes one step further than that, with 16 distinguishable voltages corresponding to values 0-15.

With each additional bit you ask an individual cell to store, you need more precision (and less speed) in both reading and writing the cell state—and less write endurance available before the cell gets too sloppy to reliably charge to and maintain a given voltage with the necessary precision.

An architectural sea change

  • The really shiny stuff is generally good news—but to the educated eye, the more interesting bits tend to be the ones shown in plain, understated gray. Samsung
  • These numbers look great—but don't miss the asterisks. Or the fact that they're in MB, not MiB, let alone GiB. Or that they "may vary based on hardware and configuration." Samsung
  • Here's where the WTFs creep in—"Storage Memory" says MLC… but it also says 3-bit. Which, to anybody who isn't a marketer, really means TLC. Samsung

Until now, Samsung's retail SSD line has been simple to understand, if you understand the basics of NAND storage. The Pro line are MLC drives—two bits per cell—with higher cost but greater speed and write endurance. The EVO line are TLC drives—cheaper, but slower and less durable. The QVO are QLC drives, and most people should likely avoid them—they aren't enormously cheaper than the TLC EVOs, but they have significant penalties to both performance and endurance.

So far, the thing most likely to confuse consumers is that the EVO line doesn't look any slower than the Pro line from reading the spec sheets. This is because the write tests Samsung uses to generate these numbers aren't particularly prolonged, and they don't burn through the SLC cache onboard the EVO. If you have a long-running write workload that fills the cache, you have to fall baRead More – Source