iMac Late 2015 - Very Slow USB ports, max 44Mb/s from any SSD or HDD

Question

iMac Late 2015 - Very Slow USB ports, max 44Mb/s from any SSD or HDD

Hello

Any SSD or Hard Drive I connect directly to the iMac USB ports has a maximum speed of 44Mb/s using Black Magic Disk Speed, whereas in the past I have seen 400Mb/s for the SSDs.

My iMac is not as responsive as it used to be. Clean install, SMC and PRAM reset, tried different cables and enclosures for the SSD and no change. One Samsung SSD I bought just a couple of months ago and will take over 20 mins to transfer a 35GB file to my iMac which has a 500GB SSD, both have plenty of free space.

Is it possible there could be a fault with the mainboard for this to happen.

Thanks

iMac 27", macOS 10.12

Posted on Feb 23, 2020 12:35 PM

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Answer 1

Top-ranking reply

rkaufmann87

Level 10

144,258 points

Feb 23, 2020 12:44 PM in response to AppleMacCider

Please navigate to the Mac App Store or navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again.

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211

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Answer 2

Feb 23, 2020 11:41 PM in response to rkaufmann87

Thanks rkaufmann87

I already have the paid for version of EtreCheck but it didn't show any major problems but it did highlight one of my SSD's was running on 10% free space (200GB) so I have now moved some of the files over to another drive. In addition I have also done a clean install and also put one of the hard drives in a powered disk caddy rather than using a USB powered enclosure and for now (fingers crossed) it seems to be working well. I will test over the next few hours and let you know of any changes, thanks again.

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Answer 3

Feb 24, 2020 2:17 AM in response to Rudegar

Yes, definitely a USB 3 port on the back of my iMac.

I think I have found the problem. When SSD connected directly to the iMac USB I am getting max read and write speeds of 44Mb/s but when connected via a decent £35 powered 7 port usb hub, I am getting 400Mb/s + for both read and write speeds. It seems there is a power issue plugging in the USBs on the Mac and can't draw enough power from them.

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Answer 4

Feb 24, 2020 1:42 PM in response to rkaufmann87

I managed to get an appointment at the local Apple store today. Without any struggle and without testing my external ssd’s the advisor offered to replace the logic board. It’s not in stock as iMac was a custom build so have to order in. Hopefully will get it back repaired in a week. So glad I have Apple Care as an expensive part to replace.

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