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The Thunderbolt 3 ports on the Touch Bar Version of the Apple 13" MacBook Pro (Late 2016) not only support Thunderbolt 3 (40 Gb/s) but also USB 3.1 Gen 2 (10 Gb/s) links to connect storage devices like the LaCie 6big Thunderbolt 3.  The LaCie 6big Thunderbolt 3 also has a Thunderbolt 3 based USB Type-C port as well as a dedicated USB 3.1 Gen 2 Type-C port.  

In a previous review, we saw that the LaCie 6big Thunderbolt 3 achieves 935 MB/sec (read) and 1055 MB/sec (write) performance over Thunderbolt 3 with the Apple 13" MacBook Pro with Touch Bar (Late 2016)'s left-side Thunderbolt ports.  Now let's see how this compares when connecting the same Mac and LaCie drive using a USB 3.1 Gen 2 link instead with the LaCie 6big Thunderbolt 3.   Again we use six 8 GB drives set up in RAID 5 mode and the AJA System Test performance tool to measure read/write performance while simulating a transfer of a 5K UltraHD resolution video file and a 16 GB test file size (note changing the file type and size can have a big impact on the results).  

First, we connect the LaCie 6big Thunderbolt 3 to Apple 13" MacBook Pro with Touch Bar (Late 2016)'s left side ports using the USB 3.1 Gen 2 capable Type-C to Type-C cable that comes with the LaCie 6big Thunderbolt 3.  Here we observe an average of 229 MB/sec (read) and 363 MB/sec (write) performance which is 24% and 34% respectively of what we observed using Thunderbolt 3.

To see if it makes a difference, we then connect the LaCie 6big Thunderbolt 3 to one of Mac's right-side USB Type-C ports.  Here we see similar same transfer speeds of 230 MB/sec (read) and 368 MB/sec (write).  Unlike Thunderbolt, there doesn't seem to be a big difference in performance between the left and right side ports.

By comparison, the LaCie 6big Thunderbolt 3's performance with Thunderbolt 3 is 935 MB/sec (read) and 1055 MB/sec (write) with the Apple 13" MacBook Pro with Touch Bar (Late 2016)'s left-side Thunderbolt ports as shown below.  

In a previous review, we also reported that the LaCie 12big Thunderbolt 3 achieved 354 MB/sec (read) and 348 MB/sec (write) over a USB 3.1 Gen 2 link on the same Mac's left side ports.  This is about 54% and 4% higher respectively than the read and write speeds observed with the LaCie 6big Thunderbolt 3.