USB-C Drives SLOW to 38mbps when plugged in with USB-3

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USB-C Drives SLOW to 38mbps when plugged in with USB-3

I purchased one of these fancy external Sandisk Extreme 2TB HDD's with a USB-C Connection for storing media on for a project. I was attracted to the 1000 Gbps speeds.

I decided to do some tests. Plugged into USB-C, the device performed as advertised: 1000Gbps read and write. However, when I switched to a USB-C to USB 3.1 cord that came included, the speeds on the same device dropped to a staggeringly low 38mbps.

After lots of troubleshooting, I found that *ANY* USB-C hard drive (I tested G-Drive, Western Digital, Samsung and my new Sandisk Extreme 2TB) plugged into my iMac using a USB-C to USB 3.1caused the device to slow down to 38mbps.

For instance, a USB-C G-Drive tested at 190mbps connected to the machine via USB-C. Connected with a USB-C to USB-3.1 cable into the iMac's USB 3.1 port--- same deal. 38mbps.

I have tried multiple cords with different lengths.

USB 3 devices plugged into the USB 3 ports perform fine. This only happens when using a USB-C to USB 3 converter cable--- again, multiple cables tested.

This explains why so many of my Final Cut Pro projects have been excruciatingly slow.

I've searched endlessly and not really found anything about this. Does anyone know what could be going on?

Specs:

2020 Retina 5K iMac

3.6 GHz 8-Core Intel Core i9

64 GB 2667 MHz DDR4

Radeon Pro Vega 48 8 GB

iMac 27″, macOS 10.14

Posted on Oct 23, 2020 2:30 PM

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Answer 1

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FMVorenkamp Author

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8 points

Oct 23, 2020 3:01 PM in response to den.thed

Thanks for the reply, but this is not accurate.

Many USB-C devices connect to USB-3 ports with a straight converter cable. This will impact performance (USB-C is much faster than 3) but not to this level of degradation.

Additionally, my cables are 3.1 compatible and have the blue bar. Nothing to do with cable incompatibility or power supply--- and adding a hub would not fix this problem, as the problem is with the OS itself.

Good News: this problem manifests after a power failure and is fixed by clearing the computer's NVRAM on startup--- problem solved!

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