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Thunderbolt vs USB3 with 6G SSD (SoftRAID, Thunderbolt v1)

OWC Thunderbay

Various configurations starting at about $499 without drives.
Thunderbay RAID-5 edition also available.

Many factors affect real world performance:

  • The speed of the “bus” over which data travels.
  • The efficiency of the chipset.
  • The inherent (or not) overhead of translating from one protocol to another, e.g., from PCIe or USB3 to SATA.
  • Drivers, operation system behavior, chipset used in the computer itself, other devices on the same bus, etc.

Thunderbolt might be expected to outperform USB3, but this is not a given for the above reasons and it can vary by enclosure, as shall be seen.


Tested with the Thunderbay IV (Thunderbolt, not Thunderbolt 2).

Tested using the same OWC Mercury Extreme Pro 6G SSD, results cross checked with a 2nd 480GB SSD. Best results are shown, both drives showed similar behavior.

The SSD was tested in these three enclosures:

Tests performed using DiskTester using the fill-volume command.

As a reference, on a native SATA bus, the 6G SSD used here delivers ~500 MB/sec. There is some variance in averages due to SSD behaviors, some of which are visible in the graph.

Native SATA 6G: 506 / 480 write/read MB/sec (NOT shown in graph here)
Firmtek ThunderTek Q6G: 378 / 497 write/read MB/sec
OWC USB3 Mini: 382 / 408 write/read MB/sec
OWC Thunderbay: 300 / 385 write/read MB/sec

The FirmTek ThunderTek PX Q6G delivers the best overall performance, including the maximum possible read performance. Its write performance is within measurement error of the USB3 enclosure. None of the solutions can match native SATA write speed.

Performance of a 6G SATA SSD is clearly seen to be a function not just of the choice of bus, but also the particular enclosure. Thunderbolt can be faster than USB3, but is not necessarily so, particularly for reads.

With the Thunderbolt-bus solutions, dual SSDs striped still have room to perform at speeds up to ~730 MB/sec because USB3 on the 2013 Mac Pro is throttled to much lower speeds. Thus, the single SSD case must be distinguished from that of a dual-SSD RAID-0 stripe, or concurrent use of dual SSDs.

Speed in MB/sec of OWC 6G SSD in OWC Thunderbay and OWC USB3 Elite Pro Mini


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