Nov 22, 2020 22:00:00

Thorough review of ultra-high-speed NVMe SSD 'WD_BLACK SN850' up to 7000MB / sec, revealing true ability in comparison with the fastest class

Western Digital has released the PCIe 4.0 compatible M.2 NVMe SSD ' WD_BLACK SN850 ', which boasts a maximum read speed of 7,000 MB / sec. We thoroughly verified how powerful the latest SSD of the company's high performance series ' WD_BLACK ' is by comparing the benchmark with 'Samsung 980 PRO ' which has similar specifications.

WD_BLACK ™ SN850 NVMe ™ SSD | Western Digital Store
https://shop.westerndigital.com/ja-jp/products/internal-drives/wd-black-sn850-nvme-ssd

◆ Appearance
The outer box of WD_BLACK SN850 looks like this. As the name suggests, the design is based on black.

Spec information etc. was written on the back side of the outer box.

According to the specifications, it is possible to access at a maximum reading speed of 7,000 MB / sec and 1 million

IOPS .

The SN850 has a lineup of models without a heat sink and models with a heat sink, and this time we will review the model without a heat sink. A model with a heat sink is scheduled to appear in 2021.

It connects to the motherboard with M.2 and transfers data using PCIe 4.0 with 4 lanes.

The back of the SN850 looks like this. There is no cooling mechanism in particular.

Since the back side of Samsung 980 PRO has a copper plate for cooling, it seems that the cooling performance will be better than 980 PRO.

WD_BLACK AN1500 As with, also SN850 Western Digital Dashboard can be performed to confirm or set various status. If you turn on the 'game mode' that can be set on the SN850, you can optimize performance and transfer data at high speed.

◆ Benchmark
WD_BLACK SN850 has different specifications such as write speed depending on the storage capacity. (PDF) The specifications are summarized in a table based on the data sheet .

	500GB	1TB	2TB	Samsung 980 PRO (1TB)
Product number	WDS500G1X0E-00AFY0	WDS100T1X0E-00AFY0	WDS200T1X0E-00AFY0	MZ-V8P1T0BW
Recording method	TLC			3bit MLC
Continuous read speed	7000MB / sec
Continuous write speed	4100MB / sec	5300MB / sec	5100MB / sec	5000MB / sec
Random read speed (4KB, QD32)	1 million IOPS
durability	300TBW	600TBW	1200TBW	600TBW
Temperature range during operation	0 ℃ ～ 70 ℃
Temperature range during non-operation	-55 ℃ -85 ℃			N / A

This time we will compare the 2TB model of WD_BLACK SN850 and the 1TB model of Samsung 980 PRO, which have similar specifications. Benchmark the SN850 in normal, game mode on, and 980 PRO to compare performance.

The specifications of the machine used for the benchmark this time are as follows.

-Motherboard : ASRock B550 PG Velocita
-CPU : Ryzen 9 3900X
・ RAM: 16GB
・ OS: Windows 10 20H2

First, measure the read / write speed with CrystalDiskMark . The continuous read speed in game mode was 7018MB / sec, and the continuous write speed was 5164MB / sec, which exceeded the nominal values. With CrystalDiskMark, there is no big difference in speed depending on whether the game mode is on or off. In comparison with the 980 PRO, the SN850 wins.

In AS SSD Benchmark , the difference in read / write speed due to turning on the game mode became noticeable.

Even with ATTO Disk Benchmark, you can see a difference in writing speed of about 100MB / sec depending on whether the game mode is on or off. In both benchmarks, the SN850 outperformed the 980 PRO in read / write speed.

The result of checking the SSD temperature immediately after the execution of ATTO Disk Benchmark is completed with

CrystalDiskInfo is as follows. The game mode can speed up reading and writing, but the temperature of the main unit rises under heavy load. You can see that the cooling performance of the 980 PRO with the copper plate is excellent.

The multi-level cell used by the SN850 and 980 PRO is a technology that can increase the capacity of SSDs at low cost, but it also has the weakness of slowing down the writing speed. In recent years, SSDs have achieved high-speed writing by using part of the memory as a single-level cell (SLC) cache in order to overcome such a decrease in write speed, but of course, when the cache is exhausted, the write speed is high. Will be slow. To see how the cache properties differ between the SN850 and 980 PRO, we will write a large amount of data using the benchmark tool

fio and check the change in bandwidth.

The parameters used when benchmarking with fio are as follows. Write large files that use the entire drive area in succession, exhaust the cache, and see how the bandwidth changes.

・ Block size: 1MB
・ Number of threads: 4
・ Iodepth: 32

Before comparing with the 980 PRO, let's first look at the capabilities of the SN850 alone. The result of writing a large amount of data via the file system is as follows.

The slowdown due to the exhaustion of cache capacity became noticeable. The cache is exhausted at an earlier timing because the game mode can write faster.

After the cache is exhausted, the write speed drops to about 1000MB / sec in both normal mode and game mode.

Normal file copy etc. is done via the file system, but OS installation etc. is written directly to the device without going through the file system. Comparing the writing speed when writing data directly to the device without going through the file system with the SN850 and when writing data via the file system, it is possible to write about 700MB / sec faster without going through the file system. ..

In this benchmark, the number of threads that write data in parallel is set to '4'. When I changed the number of threads to '1' and compared it with the case of '4', I could not confirm a big difference.

Below is a graph plotting the writing speed via the file system, with light blue as the SN850, dark blue as the SN850 game mode, and orange as the 980 PRO. The SN850 overwhelmed the 980 PRO until the cache was exhausted, and the SN850 also won the cache capacity. However, the write speed after cache depletion has risen to 980 PRO.

The speed when writing without going through the file system with SN850, SN850 game mode, 980 PRO is like this. The SN850 and 980 PRO have the same tendency as when using the file system, but in the game mode of the SN850, the result is that high-speed writing by the cache is rarely performed unless the file system is used. By that amount, we can consistently maintain a stable write speed of about 1800MB / sec.