My 2018 27 inch iMac won't boot and I need help with external SSD

I just got back from vacation and my Mac won’t start up. When I go into recovery mode, disk utility only shows the SSD part of the Fusion Drive. The HDD seems to be missing, so I think it might be dead. I tried to install the OS on the SSD, but that didn’t work. I bought a 1TB Thunderbolt drive and I’m trying to install it there, but I can’t figure out how to do that. Any suggestions?

Your Thunderbolt drive should work fine. Are you following this guide? https://support.apple.com/en-us/111336

Cody said:
Your Thunderbolt drive should work fine. Are you following this guide? https://support.apple.com/en-us/111336

I think I followed that guide. I formatted the drive and set it to journaled because APFS wasn’t available. I selected the SSD to install the OS and it let me choose it without any issues. But when I tried to install, it got stuck at 17 seconds for a long time, and then I canceled it.

What steps did you take to install macOS on the external SSD and what went wrong?

Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

Reese said:

Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

Ren said:

Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Reese said:

Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Cody said:

Reese said:
Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Yes, it is.

Reese said:

Cody said:
Reese said:
Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Yes, it is.

Did you change the View to Show All Devices? Make sure to format the top entry for the external device.

Cody said:

Reese said:
Cody said:
Reese said:
Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Yes, it is.

Did you change the View to Show All Devices? Make sure to format the top entry for the external device.

I’m not home right now, but I’ll check that. I’m not sure if I saw that option.

Cody said:

Reese said:
Cody said:
Reese said:
Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Yes, it is.

Did you change the View to Show All Devices? Make sure to format the top entry for the external device.

I looked and I don’t see that option. My drive is a Samsung T7, which should handle this easily.

Reese said:

Cody said:
Reese said:
Cody said:
Reese said:
Ren said:
Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

So you are in the Recovery Menu and going into Disk Utilities to format the external SSD as APFS, right?

I can’t format it to APFS for some reason

Is your external drive set to GUID?

Yes, it is.

Did you change the View to Show All Devices? Make sure to format the top entry for the external device.

I looked and I don’t see that option. My drive is a Samsung T7, which should handle this easily.

So you went into Disk Utility, clicked on View at the top, and then Show All Devices? Then select the top entry for your Samsung drive and click on Erase? You should see APFS as a choice.

Reese said:

Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

The Fusion Drive might be too small for macOS or it could be damaged. That can happen too.

Ren said:

Reese said:
Ren said:
What steps did you take to install macOS on the external SSD and what went wrong?

I’m trying to make an external boot drive since my internal HDD seems to have failed. It doesn’t show up at all in disk utility. I thought the SSD part of the Fusion Drive was the boot drive, but I guess I was wrong.

The Fusion Drive might be too small for macOS or it could be damaged. That can happen too.

If it was full, it would still show up as a storage device. It doesn’t show up in disk utility anymore.