Fast compact external SSDs have one major drawback: because they rely on passive cooling, they tend to get warm in use. As a result, their firmware sh

How fast SSDs slow to a crawl: thermal throttling

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2022-05-18 07:00:03

Fast compact external SSDs have one major drawback: because they rely on passive cooling, they tend to get warm in use. As a result, their firmware should slow transfer rates in order to prevent them from getting too hot – what’s known as thermal throttling. This article shows this happening during benchmarking a Samsung X5 SSD, connected to an Apple M1 Mac mini via Thunderbolt 3.

Thermal throttling should only ever be likely when writing to the SSD. In this example, I used my free utility Stibium to write a series of 96 files ranging in size from 2 MB to 2 GB, fixed sizes but in a randomised order. The test completed in a total write time of 24.4 seconds. Average transfer rate was 1.6 GB/s, but the more representative 20% trimmed mean (which excludes most outliers) was higher at 1.8 GB/s. The overall range in transfer rates was extremely wide, from 100 MB/s to 2.4 GB/s, which is typical of a fast SSD when it undergoes throttling.

Looking first at the time taken to write each of the 96 individual tests plotted against file size, there are two quite distinct linear relationships: most of the results are on the lower of the two linear trends, which shows an overall transfer rate of around 2 GB/s, with a smaller set on the upper line, with a transfer rate of slightly less than 700 MB/s. The latter results are those obtained when the SSD had throttled writes because it had become too hot to continue at full speed.

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