WD SN850 1TB

This is a fast SSD due to the full utilised SLC cache. But its performance is not sustainable when the drive is in high temperature, full-filled, or aged. Its trim performance is good. πŸ‘

WD SN850 1T

Basic Information

In this report, we compare mainstream SSDs from NAND makers: WD SN850, Samsung 980Pro, Micron/Crucial P5Plus.

Model Name Firmware Version
SN850 WDS100T1X0E-00AFY0 614900WD
980Pro Samsung SSD 980 PRO 1TB 5B2QGXA7
P5Plus CT1000P5PSSD8 P7CR403


We still check their IO latency first.

Max Write Latency

10 IOPS (ms) 4K 1QD (ms) 512B 1QD 10p filled (ms) 512B 1QD 50% filled (ms) 4K mix RW 90% filled (ms)
SN850 0.287 5.812 6.555 6.118 166.909
980Pro 8.616 8.461 8.462 14.148 42.767
P5Plus 2.273 6.604 7.559 7.914 10.797

The latency is well controlled in light workload.


Sequential Write

10% filled (MB/s) 90% filled (MB/s) 50% trimmed (MB/s)
SN850 4833.883 1649.519 3225.354
980Pro 3065.800 1796.586 2938.130
P5Plus 3675.305 1313.732 2999.762

All drives have good and similar sequential write performance. The performance all degrade when drives are full filled, and recover after trim operations.

But from diagrams below, we can find the performance of SN850 is not stable.




Random Write

10% filled (K IOPS) 90% filled (K IOPS) 50% trimmed (K IOPS)
SN850 280.283 158.988 279.883
980Pro 386.622 544.405 506.412
P5Plus 558.473 258.988 356.303

SN850 randome write performance is not as good as other 2 drives, especially when the drive is fully filled.


Except for read and write, Trim is also a common command in nowadays’ OS. We test its performance by trim half LBA space. SN850 has the best trim performance. All 3 drives can benifit performance from Trim commands.

IOPS (K) Max Latency (ms) Average Latency (ms) performance before trim (MB/s) performance after trim (MB/s)
SN850 4.184 13.649 3.804 2029.665 3225.354
980Pro 1.676 58.529 9.535 2172.154 2938.130
P5Plus 2.592 44.545 6.103 1566.011 2999.762


If we use SSD in laptop, the power consumption is also a key consideration. We list TMT1/2 setting below.

TMT1 (℃) TMT2 (℃)
SN850 80 82
980Pro 81 82
P5Plus 76 79

Low Power State

PS4 measured power (mW) PS4 exit duration (us) PS3 measured power (mW) PS3 exit duration (us)
SN850 1333.3 164.7 1332.1 164.1
980Pro 2043.0 408.1 2044.1 417.2
P5Plus 60.8 25701.3 57.0 13695.6

SN850 cannot enter PS3 and PS4 low power mode in our test. The low power data is collected after Format operation and keep idle for 2 minutes. Suppose, there should be no background jos in this condition.

Active Power Consumption



In both sequential write and sequential read test above, the temperature of SN850 rises very fast, and make the performance throttling heavily.

SLC cache retirement

SN850 use the whole capacity as SLC cache. When the drive is young and utilized space is low, it gives user the highest performance. But when the drive is aged (e.g. > 2000 P/E used), we find that SLC cache is retired, and SLC performance lasts very short time.



Data Retention

In our whole test process, we will write each DUT to its EOL (about 3000 P/E cycle for TLC SSD), then write the whole drive and keep them without power at the room temperature for 2 month. After that, we read the whole drive and verify its data integrity. Here is the test result.

Data Units Written (1000LBA) read speed 0 (MB/s) read speed 2 (MB/s)
SN850 7506783940 4941 188
980Pro 5542172462 6177 6345
P5Plus 3829583393 5599 5662

‘read speed 0’ is captured right after the data was written, and ‘read speed 0’ is captured 2-month later. SN850 was written by much more data intentionally. We check the result of ‘read speed 2’.

We intentionally write SN850 much more than other drives, so SN850 suffers more NAND raw ECC data. But it still can recover all data without any UECC error. The low speed (188MB/s) may be caused by read retry and LDPC decoder.