iMac Retina 5K 27” 2017 does not recognize USB 3.2 gen 1 stick as boot drive

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DutchImac Author

Level 1

4 points

iMac Retina 5K 27” 2017 does not recognize USB 3.2 gen 1 stick as boot drive

Hi,

I tried this with a SanDisk Extreme Pro 128GB USB 3.2 Solid State Flash Drive (USB-A Port).

https://support.apple.com/nl-nl/HT201372

For Some reason the USB flash drive doesn’t show as boot drive on my IMac.

I tried above procedure with BigSur installer and with Catalina installer. Both result in USB flashdrive not Being visible as boot drive on my IMac.

my IMac does not have a T2 chip
the USB flashdrive is visible in MacOS (Big Sur) and I Can copy data to it and read from it.
I Can also start the BigSur installation from recovery mode with the USB flashdrive as destination. This installation proceeds without an issue until it restarts. After restart it can’t find the USB flashdrive to boot from, so it can’t finish the installation.
I also tried other USB sticks, same result.
I performed a PRAM (or NVRAM) reset, no solution.
I switched off the IMac and than switched it on again with the power plug unplugged, no solution.
I deselected the setting “Ignore ownership” of the flashdrive, no solution.

I also have a Samsung X5 SSD connected to a thunderbolt 3 Port. This one works fine as a boot drive.

I Can’t find what I am doing wrong. What Can I do to enable the USB flashdrive as bootdrive of my IMac?

Thanks in advance!

iMac, OS X 10.11

Posted on Apr 27, 2021 12:02 PM

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Answer 1

Top-ranking reply

DutchImac Author

Level 1

4 points

Apr 30, 2021 1:50 AM in response to fuzzymo

I found the issue. I can’t explain it but it is related to the Samsung X5 that I have connected via the thunderbolt 3 port.

After I disconnected the Samsung X5 and I rebooted my iMac the USB sticks became visible as drives that I can select to boot from.

I was able to install MacOS Catalina on the SanDisk USB3.2 stick. After that I could boot BigSur (fusion drive) or Catalina (USB3.2 stick). After that I switched off the iMac and connected the Samsung X5 again. Still everything is working and I can boot from Samsung X5 (fast BigSur), Fusion drive (slow BigSur) and SanDisk USB3.2 stick (Catalina).

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Answer 2

fuzzymo

Level 4

2,048 points

Apr 29, 2021 2:02 PM in response to DutchImac

Just a suggestion. Make sure that you formatted the SanDisk Extreme Pro using a GUID Partition Map scheme (not Master Boot Record) and MacOS Extended (Journaled) format.

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Answer 3

Barney-15E

Level 10

122,210 points

Apr 27, 2021 12:15 PM in response to DutchImac

I also have a Samsung X5 SSD connected to a thunderbolt 3 Port. This one works fine as a boot drive.

How are the others connected? I have had issues with bootable USB installers not being recognized through a Hub.

A USB-C to A adaptor should work, but if the adaptor is a Hub, it may not work.

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Answer 4

VikingOSX

Level 10

123,356 points

Apr 27, 2021 2:23 PM in response to DutchImac

The mid-2017 27-inch 5K iMac supports USB 3.1 Gen 1 via its USB-C ports. Although USB 3.2 was announced in 2017, it did not become a standard until 2019, so this model iMac may not know what to do with this version of USB hardware, including the promise of backwards compatibility to older USB specs.

If you boot the iMac with the option key depressed, is the external Sandisk detected? Did this drive come with two cables so you can try alternate USB-C connectivity? Did you build the bootable drive using Apple's documentation?

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Answer 5

DutchImac Author

Level 1

4 points

Apr 29, 2021 1:01 PM in response to DutchImac

I tried something else today.

I have a 32GB Verbatim USB3.0 stick where I installed MacOS El Capitan on in the past for my old MacBook Pro 2009.

I plugged this USB stick into my iMac Retina 5K 27” 2017 and after that I checked If I could select it as my bootdrive.

And yes, the 32GB was in the list of devices to select as bootdrive.

I tried to boot with MacOS El Capitan, but that didn’t work. Probably MacOS is to old for my 2017 IMac.

Anyway now I know for sure that I have a device that should work as boot device on my 2017 IMac.

So I used Apple documentation (https://support.apple.com/nl-nl/HT201372) to create a bootable disk to install Mac OS Catalina.

After this was done without any errors, my 32GB USB3.0 was not visible anymore as bootdrive.

So I know for sure now that the problem is not the media (the USB stick was available as bootdevice before). It has something to do with the procedure of creating the bootable disc (USB) with MacOS installer on it.

I hope someone has an idea of what I can be doing wrong and what I can do to solve it.

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Answer 6

DutchImac Author

Level 1

4 points

Apr 28, 2021 9:07 AM in response to VikingOSX

I build the bootable drive with Apple’s documentation.

The External SanDisk isn’t detected when booting the iMac keeping the option key pressed.

The external SanDisk works fine as a drive after the IMac is booted. Shouldn’t the incompatibility with USB 3.2 be a problem then as well (not only with booting)?

Do you think a USB-A to USB-C connector could be an option to try (not included with the external SanDisk)?

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Answer 7

VikingOSX

Level 10

123,356 points

Apr 28, 2021 9:28 AM in response to DutchImac

There is nothing in that 2017 iMac that knows how to detect USB 3.2 that is two years into the future. A USB-A to USB-C adapter won't make any difference if the USB-C side is USB 3.2 for the same reason.

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Answer 8

DutchImac Author

Level 1

4 points

Apr 27, 2021 1:59 PM in response to Barney-15E

The SanDisk Extreme Pro 128GB USB 3.2 Solid State Flashdrive is directly connected to one of the USB 3 Ports (USB-A) on the backside of my IMac.

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iMac Retina 5K 27” 2017 does not recognize USB 3.2 gen 1 stick as boot drive

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