Last Week on My Mac: Why good external SSDs are faster with Apple silicon

🌈 Abstract

The article discusses the differences between Thunderbolt and USB4 in terms of their claimed maximum data transfer speeds, and how the actual performance can vary depending on the specific Mac and hardware used.

🙋 Q&A

[01] Different Macs

1. What are the key differences in the Thunderbolt and USB support between the original M1 Mac mini and a 2019 MacBook Pro?

• The original M1 Mac mini has two "Thunderbolt / USB 4 ports" that support Thunderbolt 3 (up to 40 Gb/s), USB 4 (up to 40 Gb/s), and USB 3.1 Gen 2 (up to 10 Gb/s).
• The 2019 MacBook Pro has Thunderbolt (up to 40 Gb/s) and USB 3.1 Gen 2 (up to 10 Gb/s), but does not mention support for USB4.

[02] Different up tos

1. What is the actual maximum real-world data transfer speed that can be expected from Thunderbolt 3/4 ports on Intel Macs?

• According to Intel, Thunderbolt 3 and 4 offer up to 4 lanes of PCI Express 3.0 totaling 32.4 Gb/s for general-purpose data transfer. This means the fastest real-world speed that can be expected from an Intel Mac's Thunderbolt ports is around 3 GB/s, not the claimed 40 Gb/s.

2. How does the actual performance of USB4 compare to Thunderbolt on Intel Macs?

• USB4 can support USB4 Gen 3×2, marketed as USB 40Gbps, with a nominal transfer rate of 40 Gb/s or up to 4.8 GB/s. In practice, a fast NVMe SSD connected via USB4 should achieve read and write speeds well over 3 GB/s, possibly even towards 4 GB/s.

[03] Down to 10 Gb/s

1. What can happen when connecting a USB4 enclosure to an Intel Mac?

• More recent hardware may target USB4 at 40 Gb/s but fall back to USB 3.1 Gen 2 when connected to an Intel Mac, resulting in speeds of only around 1 GB/s.

[04] Hubs?

1. How does the performance of a USB4 enclosure change when connected through a Thunderbolt 4 hub?

• With the author's Satechi Thunderbolt 4 Slim Hub, they were able to achieve 3.0 GB/s write and 3.2 GB/s read speeds with a USB4 enclosure, exceeding the speeds of a directly connected Thunderbolt 3 SSD without USB4 support.

[05] Over and out

1. What is the author's final recommendation for the best external SSDs to use with an Apple silicon Mac?

• The author recommends a high-quality USB 40Gbps enclosure, such as OWC's Express 1M2, which should reliably provide over 3 GB/s performance, even when connected through a compatible hub. This is preferred over the "up to 3 GB/s" performance of Thunderbolt 3 enclosures on Intel Macs.