Unable to format external SSD using Utility

Question

Unable to format external SSD using Utility

I have a 2019 iMac 4K Retina, 21.5inch iMac that is running very slow.

I read in the community that installing an external SSD might resile this and I bought the LaCie Mobile SSD secure, 1TB.

I'm trying to follow the Utility instructions to format a SSD drive as APFS.

I get as far as completing its number 4 - erasing the disk.

Number 5 says "Click the Scheme pop-up menu, then choose GUID Partition Map". I've not been able to find any way to get this pop-up menu to appear.

I saw a similar post but no solution.

In utility I can view all drives and I have erased the external LaCie mobile and the sub to this that says untitled.

When I right click on the "untitled" It has an option to "convert to APFS"

I clicked on this but it failed and the message was that the operation failed.

"A GUID Partition Table (GPT) partitioning schemer is required

Is anyone able to assist?

I have no third party anti virus running and the system is Sonoma 14.5

iMac 21.5″, macOS 14.5

Posted on Aug 2, 2024 1:08 AM

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Answer 1

Top-ranking reply

MartinR

Level 7

25,480 points

Aug 2, 2024 7:03 AM in response to charlesoconnor

In Disk Utility, make sure that you set View > Show All Devices.

Then in the left pane under External select your Lacie drive's topmost icon. It should have the word "Media" appended to the name. (This is the physical drive, the device that needs to be GUID partition type. What you called the "sub" is not the physical drive.) Then click the Partition button, select GUID partition and format APFS.

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Answer 2

Aug 2, 2024 2:59 PM in response to charlesoconnor

Ok, I have got it.

When I erased the extended drive I did not have the correct information in the drop down menu.

i.e. APFS and GUID

Thanks again for your help

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Answer 3

den.thed

Level 10

93,798 points

Aug 2, 2024 9:49 AM in response to charlesoconnor

Eject and disconnect the external drive.

Restart the iMac, reconnect the external drive.

Open Disk Utility, then try reformatting the external drive.

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Answer 4

den.thed

Level 10

93,798 points

Aug 2, 2024 7:38 AM in response to charlesoconnor

MartinR is spot on.

also see > "Connect and erase the external SSD" at > Use an external SSD as your startup disk … - Apple Community

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Answer 5

Aug 2, 2024 8:58 AM in response to MartinR

Thanks Martin, I really appreciate your advice.

I have selected the topmost icon for the LaCie drive in the left pane under external but the partition button is greyed out?

I did erase this drive as I said in my email.

Is there a way to reinstate this greyed out partition button?

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Answer 6

Aug 2, 2024 9:00 AM in response to den.thed

Thanks to you also Den,

I had followed the directions as per your link and as I said in my original posting when I got to step 5 of those instructions (after erasing the external drive) there is no "scheme pop up menu"?

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Answer 7

Aug 2, 2024 2:51 PM in response to den.thed

Hello Den,

thanks for your response.

I did as you suggested and the partition button is still greyed out when I click on the External hard rive in disc utility?

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Answer 8

den.thed

Level 10

93,798 points

Aug 2, 2024 4:51 PM in response to charlesoconnor

👍 Good work.

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Unable to format external SSD using Utility

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