TB3 port speed showing 20 Gb/s x1

I have a Mac Mini with attached Drobo 8D (with provided TB cable). System Information reports the device is connected at “20 Gb/s x1” which seems to be a TB2 speed, versus a TB3 speed. The
[http://www.drobo.com/downloads/products/1118-01-8D-DS.pdf](http://Drobo 8D Data Sheet)
states achieve throughput by enabling the bi-directional 40 Gbps performance of Thunderbolt 3. Perhaps that is marketing speak meaning 20 Gbps * 2 directions = 40 Gbps? I realize that my disk performance is the limiting factor here, but am wondering if the 20 Gb/s x 1 connection is also going to limit any downstream (daisy-chained) TB3 devices I might add. I do have another TB3 device (on a different TB3 port), which shows the expected “40 GB/s x1” speed. The system information does show a 2nd port at 40 Gb/s x1, so perhaps the 8D link speed is not a factor for downstream devices?


Is this the expected port speed for the 8D? Contrast to another TB3 device:


I thought I read in a review of the 5D3, that Drobo supplied a Thunderbolt 2 speed cable. Do you have another cable you can try?

I noticed that as well (after the fact!). I just ordered a new cable, and will give it a try when received.

Yes, it was the cable indeed. The supplied cable registers 20Gb/s, but an Apple Thunderbolt 3 cable registers at 40Gb/s.


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