Samsung released a performance document for its SZ985 Z-NAND SSD. The new SSD uses a special flavor of Samsung's flash to offer unheard of performance from a NAND-based SSD, with the obvious intention of offering good-enough performance at a much lower price than Intel's DC P4800X Optane SSDs. For now, Samsung is pushing the SZ985 to its data center customers, but much like Intel does with its 3D XPoint-based SSDs, we could see a consumer version come to market for the enthusiast crowd.
Samsung's document laid out some rather impressive performance specifications for the new drive, but they're limited in scope. The Z-NAND SSD boasts up to 3.2 GB/s of sequential read/write throughput and 750,000/170,000 random read/write IOPS. The random read specifications are impressive compared to other NAND-based SSDs, but we have to take the measurements with a grain of salt.
Samsung spec'd the 3D TLC PM1725a at over 1 million random read IOPS but has never submitted the SSD for review and doesn't specify the type of workload it used to measure random read performance. We've seen independent third-party tests that put the number closer to ~700,000 IOPS with an industry-standard 4K random test.
| Header Cell - Column 0 | Samsung SZ985 Z-NAND SSD | Intel Optane (3D XPoint) | Samsung PM1725a | Intel DC P3700 |
|---|---|---|---|---|
| Interface | PCIe 3.0 x4 | PCIe 3.0 x4 | PCIe 3.0 x8 | PCIe 3.0 x4 |
| Media | Z-NAND | 3D XPoint | 48-layer 3D TLC NAND | 20nm MLC NAND |
| Sequential Read/Write (GB/s) | 3.2 / 3.2 | 2.4 / 2 | 6.4 / 3 | 2.8 / 2 |
| Random Read/Write IOPS | 750,000 / 170,000 | 550,000 / 500,000 | 1,080,000* / 170,000 | 460,000 / 175,000 |
| Random Read Latency | 12 - 20µs | 10µs | 90µs | 115µs |
| Random Write Latency (typ) | 16µs | 10µs | 20µs | 25µs |
| Drive Writes Per Day (DWPD) | 30 | 30 | 5 | 17 |
| Capacity | 800 GB | 350 / 750 GB | 1.6 / 3.2 / 6.4 TB | 400 -800 GB / 1.6 - 2 TB |
However, Samsung's claimed latency reduction is striking. The company said the SZ985 delivers 12-20µs latency for random reads and 16µs for random writes. These latency numbers are particularly strong compared to the other NAND-based SSDs in the table, although they aren't quite as mind-bending as Intel's Optane. The SZ985's random write performance also lags behind the Optane DC P4800X, but Samsung's strategy is to offer good-enough performance at a much lower price point. In the enterprise, cheap and "good-enough" almost always wins.
Samsung also provided performance results compared to its PM1725a in RocksDB workloads, along with a few synthetic performance measurements. We also included a picture of the company's performance data displayed at the Flash Memory Summit. The latency-to-IOPS comparisons highlight similarly solid low-QD performance scaling compared to Intel's Optane SSDs.
From the limited data, the SSD looks impressive, but there are still several unanswered questions. Samsung hasn't released QoS metrics, such as 99th percentile performance, that are a strength of 3D XPoint-powered SSDs. The company also hasn't released the mixed random workload specifications, which are a critical aspect of real-world application performance. Given the SZ985's NAND-like random write IOPS specification, we imagine it wouldn't fare as well during mixed workloads. The latency scaling chart, for instance, only measures performance with a random read workload, but the SSD might not scale as well when a mixture of random writes are added to the equation. We expect more information to trickle out as the SSDs come to market.
The SX985's endurance is impressive. In fact, its 30 DWPD of warrantied endurance rivals Intel's Optane SSDs. Samsung hasn't released detailed information about its Z-NAND, but it has confirmed our early speculation that it uses MLC NAND in an SLC configuration. That provides both performance and endurance boosts, but it's likely that Samsung's references to a "unique circuit design" means shorter bitlines and wordlines in the NAND package, which would improve performance. It's also possible that the NAND die have more planes, which are sections of the die that respond independently to data requests, to boost performance. We also know the company is using a new controller.
Samsung also revealed that it has an MLC variant in the works that will offer slightly less performance but much more capacity. That indicates the SZ985 isn't a one-off product and that we'll see further development in the future.
Samsung's strategy of leveraging proven and mature NAND technology is smart, particularly due to economics. Lowering the price of any new memory requires scale, and that's a process that can take years. In fact, Intel and Micron just announced last week that they have expanded 3D XPoint production, although we suspect that some of the expansion is targeted at the second generation of 3D XPoint, which many expect to come along sometime next year. In contrast, Samsung already has copious NAND fabrication capabilities, so spinning up a new version of NAND likely doesn't require extensive investments and should foster widespread availability.
Price will be key to Z-NAND's success. Most existing applications cannot fully utilize the performance of Intel's 3D XPoint-based SSDs, so providing enough performance to get within range of Optane's usable performance at a lower price point could be disruptive to Intel's ambitions. Unfortunately, we aren't sure of pricing or availability yet.
