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: