One thing that often catches-out Mac users is that when they buy an external SSD hard drive, they don’t get the maximum data transfer speeds that the drive is supposed to be capable of.
Surprising as it may sound, even the latest Apple Silicon Macs don’t support the the fastest USB 3.2 Gen 2×2 standard which is capable of transfer speeds of up to 20Gb/s (2500MB/s).
Although USB 3.2 Gen 2×2 uses the same USB-C/Thunderbolt ports that all Macs have, the actual transfer speeds you get are very different.
That’s why we always advise users to buy Thunderbolt external drives for Macs as Thunderbolt is the only standard that provides the maximum transfer speeds the drive is capable of when connected to a Mac.
Here we explain why so you don’t get disappointed when choosing an external hard drive for your Mac.
Why Don’t Macs Support The Fastest USB Connections?
Some of the most popular external drives on the market now support USB 3.2 Gen 2×2 which is basically an ultra fast USB 3.2 connection with dual lanes.
An example is the SanDisk Extreme Pro which is one of the fastest and best value SSD drives you can get.
- Powerful NVMe solid state performance featuring up to 2000MB/s read/write speeds.(1) (Based on internal testing; performance may be lower depending on host device, interface, usage conditions and & other factors. 1MB=1,000,000 bytes.)
- A forged aluminum chassis acts as a heatsink to deliver higher sustained speeds in a portable drive that’s tough enough to take on any adventure.
- Up to 3-meter drop protection and IP65 water and dust resistance(4), and a handy carabiner loop. (Previously rated for 2-meter drop protection and IP55 rating. Now qualified for the higher, stated specs.)
- Help keep private content private with the included password protection featuring 256‐bit AES hardware encryption.(3)
- Easily manage files and automatically free up space with the SanDisk Memory Zone app.(5) (Download and installation required.)
Although you can physically connect it to a Mac, the drive only works at around half the speed it is capable of with Macs.
The reason is because USB 3.2 2×2 supports 2 lanes of data going at 10Gb/s both ways to reach the maximum speed of 20Gb/s.
Macs on the other hand (and in fact still many PCs too) can only support one lane of data flow through USB 3.2 2×2 cables.
This means you will only get USB 3.1 Gen 2 speeds on a Mac i.e. 10Gb/s via one single lane.
Any USB-C external drive that supports USB 3-2 2×2 will therefore claim to offer up to 20Gb/s read/write speed but that’s only true if your computer supports it.
The Thunderbolt 4 ports in the latest Apple Silicon Macs don’t support the maximum speed of the USB 3.2 2×2 standard because the technologies used in USB 3.2 2×2 and Thunderbolt are slightly different.
Therefore Mac users using the SanDisk Extreme Pro SSD drive on any Mac will only get around half the advertised transfer speed of 2000 MB/s.
This is still pretty fast though and means you should be able to transfer an 85GB file to a USB 3.2 2×2 external drive in just under 2 minutes. But it’s disappointing considering you’re only getting half the drive’s capable speed.
In reality as well, the read/write speeds will be even slower than this due to the way the hard drive throttles speeds to prevent over heating and the size of something known as the SLC cache.
It’s therefore possible that you’ll see transfer speeds of between 700-800 MB/s on a Mac with a USB 3.2 2×2 external hard drive such as the SanDisk Extreme Pro as you can see in the test below.
Why Thunderbolt Drives Are Faster With Macs
Whenever we purchase a new external drive at MacHow2, we always go for a Thunderbolt compatible drive.
Thunderbolt was initially developed by Apple and Intel back in 2009 under the name “Light Peak” and soon became a standard connection port on Macs.
Because Thunderbolt connections are fully compatible with Macs, you get the maximum transfer speeds that the drive is capable of – or at least close to.
The latest Thunderbolt 4 ports such as on the M3 MacBook Pro and M2 Mac Studio can theoretically achieve incredibly fast speeds of 40Gb/s (5000MB/s).
That’s capable of transferring a 50GB file from your Mac in less than a minute which is pretty amazing.
In reality, most Thunderbolt drives can’t reach these maximum speeds due to physical performance limitations of the drive (they will literally burn-up with the heat generated) but you’ll still enjoy read speeds of around 2800MB/s and write speeds of 2400MB/s.
This is at least twice as fast as anything you will get with a USB 3.2 Gen 2×2 drive.
Although there are fewer Thunderbolt compatible hard drives on the market, there are now some excellent external Thunderbolt drives out there.
The best value option is the SanDisk Extreme Pro G-40 SSD which promises speeds of up to 3000MB/s (although the reality is you’ll get around 500MB/s less than this).
- Super-fast speeds up to 3000MB/s(1) read and 2500MB/s(1) write with Thunderbolt 3 (40Gbps), capable of moving 50GB in 1 minute or less
- Dual-mode compatibility with both Thunderbolt 3 (40Gbps) and USB-C (10Gbps)
- Ultra-rugged design with high-level IP68 dust/water resistance, 4000lb crush resistance, and 3m drop resistance (On a carpeted concrete floor.)
- Cool aluminum core pulls heat away from the internal drive to help maintain super-fast transfer speeds
- Pro-grade enclosure for premium strength you can feel
Previously, the best Thunderbolt drive was the pricey Samsung X5 although Samsung has unfortunately discontinued it.
The world of connection ports is confusing and it’s no wonder that some Mac users get caught-out by the different connection standards when buying an external hard drive.
For more, check out our guide to Thunderbolt vs USB-C ports for a more in-depth explanation of the difference between them.
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