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External SSD read speed low through Mac mini USB-A

Hello, I've been running a few tests on SSD speed and I was surprised by the results.

Connecting both a crucial x6 and a crucial x8 to the Mac mini USB-A port gave very slow speed results

Write: 417 MB/s and Read: 48 MB/s

Connecting the same disks through the Thunderbolt 4 port however gave results closer to theoretical limits of the above SSD (800 MB/s) for both write and speed.

This is expected of course, T4 is faster, but I don't understand why the lower read speed compared to the write speed when using USB-A

Is there something in the USB-A architecture that justifies those slower speed in read?

Many thanks

Mac mini

Posted on Oct 8, 2023 8:13 AM

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valevari Author

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Posted on Oct 9, 2023 1:03 PM

Nope I was wrong...

I did further testing and realised the problem it's a usb hub connected to the other USB A port, I tried different ones, all powered, and every time I connect one, the other USB A port where an SSD is connected suffers, if I remove the hub and all goes back to normal.

If I connect 2 SSD to each USB A port, everything is fine too.

I'm really baffled, I wold have never thought that a hub connected to one port could influence the other.

Are usb hub generally rubbish with my particular set up? Shall I keep looking for a different hub? Or do I have and hardware problem (diagnostics said no for what is worth)

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BDAqua

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Oct 8, 2023 4:38 PM in response to valevari

Connecting a really cheap SSD via USB3.1 on 2019 iMac, I get 406 MB/s & 417 MB/s write.

valevari Author

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Oct 10, 2023 11:46 AM in response to BDAqua

not sure what you mean but the usb hubs were powered by their own AC power

BDAqua

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Oct 10, 2023 2:29 PM in response to valevari

Do your USB hubs have a cord that plugs into the wall,, or just plugs into the computer for power?

valevari Author

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Oct 13, 2023 1:13 AM in response to BDAqua

powered through a wall adapter

valevari Author

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Oct 13, 2023 9:31 AM in response to Rudegar

to remove this hypothesis I tried with 3 different brand new powered usb3 Gen 3.2 hubs, rated for 10Gbps and sadly the results are the same

Oct 11, 2023 5:39 AM in response to valevari

Just a check, what version of macOS are you running? Make sure you are running the latest version of macOS. Each macOS update also includes firmware updates which may be part of your issue.

FWIW, this is an odd issue I have not seen on any computer with USB hubs.

BTW, is this occurring only with this particular drive or does the issue happen with all drives? Some DIY case/drive combinations can sometimes operate oddly in certain situations and connections.

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External SSD read speed low through Mac mini USB-A