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USB 3 drive runs at USB 2 speed after reconnecting

There’s something going on with my MacBook Air and external devices wherein external hard drives run at usb 2 speeds, around 30 MBps The weird thing is that if I restart my Mac with the hard drive connected, it goes back to the usual usb 3 speeds, around 90-100 MBps. Ejecting the hard drive and plugging it back in makes it go back to usb 2 speeds again. My only solution to this is leaving my hard drive connected at all times. Is this a bug in macOS or something else? I've been experiencing this since macOS 11.3 or 11.3.1. My hard drive configuration is a SATA to USB C adaptor. Another thing that I noticed is that the Hard drive uses the first usb bus, which makes my hard drive run at usb 3 speeds, and in the description, it's speed says 5gbps . After disconnecting and reconnecting, it switches to the second USB 3.1 bus and makes my hard drive run at usb 2 speeds, and now the description says that the speed is 480 mbps.

MacBook Air (2020 or later)

Posted on Jun 16, 2021 6:14 PM

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12 replies

Jun 16, 2021 6:54 PM in response to NightWest

NightWest wrote:

But the weird part is that, if I connect it to another Mac, it doesn't have the same problem.
I connected it to a 2016 MacBook Pro. I'm starting to think its the T2 chip causing this? And the fact that restarting makes it go back to USB 3 speeds seems weird too.



Try resetting NVRAM/PRAM http://support.apple.com/kb/ht1379


Jun 17, 2021 6:37 AM in response to NightWest

Have a similar issue running through my hub. When I connect a bus powered SSD to one of the USB 3.1 gen 2 ports it runs at 2.0 speeds or does not even connect. If I power down the Mac (or the hub) and restart it shows 3.1 gen 2 speeds. If I connect the same SSD using a self powered dock I have no issue. It appears if the drive is pulling too much current from the bus it will not connect or it connects at the slower speeds. Not sure this applies to you but seems similar if not the same issue.

Jun 17, 2021 7:44 AM in response to NightWest

Alright, so I found a temporary solution to this. I have an official Apple usb c to usb a dongle and I also have this adaptor which converts usb c to a, an adaptor that comes with a SanDisk Extreme External SSD. I plugged them all together and fixed the problem. I know it does defeat the purpose of buying a USB C adaptor and still need to use a dongle but that is the only solution that I can find right now.

USB 3 drive runs at USB 2 speed after reconnecting

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