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Thunderbolt vs USB3 Performance as RAID-0 Stripe
To assess Thunderbolt vs USB3, a RAID-0 stripe configuration was used (double capacity, double speed vs a single drive metric).
A 1TB partition was made on the fastest 1/6 0f the drives (3 X 2TB = 6GB) in order to compare Thunderbolt to USB3 speed.
The drives were Toshiba 3TB, about as fast a hard drive as can be found, delivering peak speed of 170 to 180MB/sec on the very fastest side of the drive, hence the most that can be expected is 340 - 360 MB/sec in a dual-drive RAID-0 stripe.
Performance for many tasks revolves around sustained transfer speed (e.g. saving large Photoshop files). Anything requiring very high transaction rates (many small reads and writes) is better approached with a fast SSD.
Both Thunderbolt and USB3 deliver to twice the speed of a single drive in a RAID-0 stripe configuration (very fast and as good as can be achieved).
USB3: 355, 358 write/read MB/sec
Thunderbolt: 344, 356 write/read MB/sec
USB3 performs marginally better than Thunderbolt, discussion continues below.
The Thunderbolt test was run twice; as shown this is the best-of-two runs (even a little more variation was seen with one run).
It turns out that USB is not only just as fast, but offers a slightly tighter performance envelope; the write speed variation with Thunderbolt is more (red line). In real world use, this is inconsequential.
Possible theory on Thunderbolt vs USB3 speed:
USB logic steps:
Drive > SATA to USB controller > USB cable > USB host/chipset
TB logic steps:
Drive > SATA to PCIe controller > TB controller > TB cable logic > cable > TB cable logic > TB Host controller