Introduction

Western Digital (or simply WD) is the world's largest manufacturer of storage solutions, mostly known for their wide range of hard disk offerings. With their acquisition of SanDisk in 2016, WD became one of the largest manufacturers for flash storage, too.



In this review, we're checking out the WD Black SN770M, a remarkably compact M.2 NVMe drive adopting the 2230 form factor, with a mere 30 mm length. Its compact size makes it a perfect match for the Valve Steam Deck. Moreover, the SN770M is an option for expanding the storage on the ASUS ROG Ally game console and various Microsoft Surface Pro devices. Of course the drive will also fit into cases where an M.2 2242 PCIe drive has to be used.

In recent weeks we have reviewed several other M.2 2230 SSDs, which are all based on the same hardware design from Phison: a Phison E21 controller is paired with Micron 176-layer 3D QLC NAND flash. The WD Black SN770M is completely different. It uses only in-house components made by WD/SanDisk. The heart of the drive is the controller, which is the same 20-82-10081 that we've seen on the full-length WD SN770. The NAND flash is BiCS5 using 112-layer TLC technology. This is a major difference to the competing drives on the market, which are mostly QLC. As expected, a DRAM cache chip is absent due to space limitations, the SN770 (without M) is DRAM-less, too. The drive interfaces with the rest of the system through the PCI-Express 4.0 interface.

The WD Black SN770M is available in capacities of 500 GB ($80), 1 TB ($110) and 2 TB ($220). Endurance for these models is set to 300 TBW, 600 TBW and 1200 TBW, respectively. WD includes a five-year warranty with the SN770M SSD.

Packaging

The Drive

The drive is designed for the highly compact M.2 2230 form factor, which makes it 22 mm wide and only 30 mm long.


PCI-Express 4.0 x4 is used as the host interface to the rest of the system, which doubles the theoretical bandwidth compared to PCIe 3.0 x4.


On the PCB you'll find the SSD controller and one flash chip. A DRAM cache is not available.

Chip Component Analysis

Almost nothing is known about the SanDisk 20-82-10081-A1 SSD controller. It is a four-channel design, which obviously supports TLC and DRAM-less operation. It is used on drives like the SN770, SN770M and SN740. It has support for the fast PCI-Express 4.0 interface.


The flash chip is 112-layer Kioxia/Toshiba BiCS5, rebranded by SanDisk, who are now part of WD. WD operates a joint-venture with KIOXIA to produce these NAND chips.

Test Setup

Synthetic Testing

• Tests are run with a 20-second-long warm-up time (result recording starts at second 21).
• Between each test, the drive is left idle for 60 seconds, to allow it to flush and reorganize its internal data.
• All write requests contain random, incompressible data.
• Disk cache is flushed between all tests.
• M.2 drives are tested with a fan blowing on them; that is, except for the results investigating uncooled behavior on the thermal testing page.

Real-life Testing

• After initial configuration and installation, a disk image is created; it is used to test every drive.
• Automated updates are disabled for the OS and all programs. This ensures that—for every review—each drive uses the same settings, without interference from previous testing.
• Our disk image consumes around 600 GB—partitions are resized to fill all available space on the drive.
• All drives are filled with random data to 80% of their capacity
• Partitions are properly aligned.
• Disk cache is flushed between all tests.
• In order to minimize random variation, each real-life performance test is run several times, with reboots between tests to minimize the impact of disk cache.
• All application benchmarks run the actual application and do not replay any disk traces.
• Our real-life testing data includes performance numbers for a typical high-performance HDD, using results from a Western Digital WD Black 1 TB 7200 RPM 3.5" SATA. HDDs are significantly slower than SSDs, which is why we're not putting the result in the chart, as that would break the scaling, making the SSDs indistinguishable in comparison. Instead, we've added the HDD performance numbers in the title of each test entry.