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I have two PIs: Pi 2 Model B v1.1, and Pi 3 Model B.

Both Pis are running with defaults. Also, both Pis are each powered by a 2A supply.

I also have an externally powered hard drive dock that happens to be USB 3.0. I understand that neither of my Pis have USB 3.0 support, that's not the issue.

I discovered that if I plug the dock into the Pi 3 using a USB 3 cable, the drive is not recognized by the Pi (no new device shows up in dmesg or lsusb).

However, if I plug the dock into my Pi 2, even with the USB 3 cable, it is recognized and I can even mount/access the drive.

Since I needed the disk to be mounted on the Pi 3, I was able to mount the drive by instead using a USB 2.0 cable.

The question: Why would the USB 3 cable work with the Pi 2, but not the Pi 3?

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    There is no logical reason. A USB3 cable has 9 pins, the 4 standard USB2 pins plus 5 others. The Pi2/3 USB ONLY has the matching 4 pins, so either cable should work.
    – Milliways
    Feb 6 '17 at 4:31
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As mentioned in the comments, there is no easy logical explanation right off the bat. Both the RPi2 and RPi3 use the same USB controller (LAN9514, see here). Unless there are material differences between the actual USB ports between the RPi2 and RPi3 (which I doubt), this may be an OS issue.

Which OS's are you running on both?

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  • Both Pis are running Raspbian 8. The Pi 3 has kernel 4.4.38-v7+, and the Pi 2 has kernel 4.1.13-v7+. Feb 7 '17 at 17:59

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