Because of the robust statistical methods used to analyse individual test results, this still yielded reproducible data, and is a good illustration of the importance of sound and robust analytical methods when measuring disk performance.

To ensure that throttling didn’t occur during testing, the amount of data written was limited to 10 GB in each test. Testing was performed using a Samsung X5 SSD, which is known to throttle after relatively small amounts of data have been written to it. This article assesses whether similar problems afflict the Thunderbolt 4 ports on later models of MacBook Pro with M1 Pro or Max chips. Moreover, it wouldn’t be consistent with theory proposed by OWC to account for the problems in original M1 Macs, which is dependent on them only supporting a single display. If that were to be correct, it would be of even greater consequence, as those models support multiple external displays including Apple’s new Studio Display. Since that report a year ago, there have been various rumours about similar issues affecting later M1 models including those using M1 Pro and even M1 Max chips. This doesn’t appear to affect read performance, though, only write. If you use an original M1 Mac with an external SSD and have the option of connecting its display by HDMI or Thunderbolt, it’s now clear that it’s worth checking to see whether using Thunderbolt for the display might also improve write performance to the SSD.

OWC engineers discovered that these could be improved to around 1.8 GB/s by connecting the Mac to a Thunderbolt display, and kindly wrote this up on the OWC blog. Examples quoted include speeds as low as 1.0-1.1 GB/s for OWC Envoy Pro models. Among issues reported in Apple’s original M1 Macs were poor write speeds to external SSDs in certain configurations.

Mac mini m1 thunderbolt 4 hub