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How fast is USB 3.0 really?

James Galbraith | May 27, 2013
Now that USB 3.0 is found on (almost) every new Mac, the Macworld Lab decided to put its real-world speed to the test, especially compared with FireWire 800 and Thunderbolt.

Our tests included timing how long it took to copy a 10GB file to the external drive (in other words, to write the file) and then to copy that file back to the internal drive (read the file). We ran a similar test with 10GB worth of smaller files and folders. Finally, we ran Aja Video Systems' Aja System Test, a free benchmark that's meant to see how fast your system is and how it would perform under different video-editing circumstances. We used the 2GB File setting with 1920 by 1080, 10-bit, RGB frame sizes.

table comparing speeds

Our USB 3.0 tests were pretty consistent. Regardless of which test we ran or how we connected the drive, all of our USB 3.0 results were in the range of 112 MBps to 115 MBps range. The Aja System Test Write scores were a little slower with the Hitachi drive connected directly to a USB 3.0 port on the MacBook Pro--107.2 MBps; through the Belkin hub, the score was 106.1 MBps, and with the StarTech hub, the score was 102.5 MBps.

(We also ran the tests again with the USB 3.0 drive connected to the hubs along with a USB 2.0 keyboard and mouse attached to the hub to see if that would affect performance. We didn't see any performance differences with the USB 2.0 peripherals attached, so I didn't include the results in the charts.)

Our USB 2.0 results were also very consistent, topping out at 41 MBps in each of our six tests. Interestingly, the write speeds for the files on folders tests were faster using the hubs, going from 35.1 MBps when connected directly, to about 41 MBps through the hubs.

FireWire 800 was about half as fast as USB 3.0 in our write tests, turning in scores ranging from 55 MBps and 60 MBps. The read scores were faster, though at 72.3 MBps and 74.5 MBps, they were still considerably slower than USB 3.0.

Thunderbolt turned in scores nearly identical to the USB 3.0 results, showing that the 7200-rpm drive was acting as a bottleneck to faster transfer speeds.

SSD tests
To try and remove the spinning-hard-drive bottleneck, we ran the same tests, but with an OWC Mercury Extreme Pro 6G SSD as the external drive. Again, USB 2.0 results were slow and consistent. We saw the same 40-MBps scores across all tests, with or without the hub. In this case, USB 2.0 was the bottleneck.

USB 3.0 speeds, on the other hand, definitely benefited from the faster performance of the SSD. When writing the 10GB file, the USB 3.0 connection hit nearly 200 MBps. We saw similar results with Aja System Test's write tests. Aja and file-read test results were a little slower--167 MBps--while reading a folder with 10GB of smaller files took just about 160 MBps. The slowest score for USB 3.0 and the SSD was for writing the folder of many small files, which it did at 144.7 MBps.


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