Thermal Throttling

Due to the compact form factor, M.2 drives lack the ability to cool themselves and usually have to rely on passive airflow instead. All vendors include some form of thermal throttling on their drives as a safeguard, which limits throughput once a certain temperature is exceeded.

On this page, we will investigate whether the tested drive has such a mechanism, how high temperatures get, and what effect this has on performance. We will test the drive in a typical case and the M.2 slot between the CPU and VGA card. A second data point shows the result with a 120 mm fan directly blowing on the tested drive. Each of the charts has time moving from left to right, with the blue line displaying transfer speed in MB/s and the red line showing the temperature in degrees Celsius (measured using SMART).

Results from this test setup are not comparable to our 2019 SSD bench because we're using a different case and a CPU cooler that generates some airflow around the CPU socket.

Reads

Writes

All the write charts show some slowdown from time to time, roughly every three minutes, but that's not thermally related because it's also present in the fan-cooled results, making it temperature-independent. We also saw the exact same pattern on other QLC drives using the E16 controller.

Without heatsink or heatspreader, the uncooled drive will run at maximum speed for roughly one minute before thermally throttling. In that time, 200 GB of data are written, which is plenty for nearly all scenarios. When we add the heatspreader foil, we see a similar timing—a minute, then throttling starts, but instead of 1.8 GB/s sustained, we're now getting 2.5 GB/s—quite a significant difference. In a third test, we installed the heatsink, and removed the heatspreader to not trap heat. Results show that the added mass of the heatsink can soak up more heat, which means throttling happens much later in our test, after around four minutes. At 2.6 GB/s, maximum write speed is comparable to the heatspreader test.

Thermal Image & Hot Spot

The thermal images confirm our findings.