I've read it will only work with usb 3.0, I ordered a 3.0 cable today just to have one, curious, this guys says 2012 should work with usb, but we know about believing stuff off the internetJust checked my 2015'ish MBP Retina. Only offers TB when powered up in TDM. I can't find a USB A-A cable to try to see if it works. From what I remember i've only ever been able to have USB in TDM when that is the only available port on the machine.
Target Disk Mode over USB only works when connected via USB 3, so it can only be used with 2012 and later Macs (despite Apple’s support article erroneously suggesting older models, by stating “any Mac”). Nor can Target Disk Mode be used with Apple’s USB-C charge cable, which is a USB 2 cable when used for data.
So, to use Target Disk Mode over USB, you can use:
- a USB 3 C-to-A cable if connecting to a Mac with USB-A ports (most Macs)
- a USB 3 C-to-C cable if connecting to a Mac with USB-C ports (MacBook 12″, 2016 MacBook Pro)