What drive to erase on a Fusion Drive 2017 iMac?

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What drive to erase on a Fusion Drive 2017 iMac?

I need to know exactly how to erase (format) a Fusion Drive iMac using Recovery Mode and Disk Utility.

I don't know whether to erase the Fusion Drive itself (at the top of the hierarchy on the top left), or to erase the Container Disk (second in the hierarchy) or to erase the Macintosh HD (last in the hierarchy).

Info: 2017 iMac, 21.5 inch, Monterey, intel based, without T2.

My goal is to perform a factory reset (by erasing the correct drive) so that I can reinstall macOS. Would erasing any of the three drives and reinstalling macOS on said drive do the job?

I wasn't provided with the Apple ID password of the previous owner. Would this reset erase that Apple ID account and everything related to it so that I can use the iMac as brand new?

Many answers to questions of this topic just link to standard instructions that don't address my specific concern.

Please, any help would be greatly appreciated.

iMac (2017 – 2020)

Posted on Jul 12, 2023 12:26 PM

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Answer 1

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Tesserax

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151,827 points

Jul 12, 2023 12:50 PM in response to AndreasBlack

Firstly, you'll want to erase the Fusion Drive itself, which is at the top of the hierarchy in Disk Utility. This will ensure that all data, including the operating system, is completely removed from the drive. After erasing the Fusion Drive, you can then reinstall macOS.

Here are the basic steps to follow:

1. Restart your iMac and immediately press and hold Command (⌘) and R to start up from macOS Recovery.

2. When you see the macOS Utilities window, choose Disk Utility and click Continue.

3. In Disk Utility, select your Fusion Drive from the sidebar. It should be the first item in the hierarchy.

4. Click the Erase button in the toolbar. If you see a Scheme option, choose GUID Partition Map.

5. Choose Mac OS Extended (Journaled) as the format.

6. Click Erase to begin the process. This will take some time, so be patient.

7. After the process is complete, quit Disk Utility to return to the macOS Utilities window.

8. Now, select Reinstall macOS and follow the onscreen instructions to reinstall the operating system.

As for the Apple ID of the previous owner, erasing the Fusion Drive will indeed remove all data related to that Apple ID. However, you'll need to enter your own Apple ID during the macOS reinstallation process to set up the App Store and other services.

Ref:

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Answer 2

AndreasBlack Author

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Jul 12, 2023 1:33 PM in response to Tesserax

Thank you for help. I have one last question. If I’m unable - for whatever reason - to erase the Fusion Drive itself on the top of the hierarchy, which of the other two (container disk or Macintosh HD) should I try to erase? And would it work the same as if I had erased the Fusion Drive?

I’m only asking for specifics because there are many contradictory instructions out there.

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Answer 3

Tesserax

Level 10

151,827 points

Jul 12, 2023 1:43 PM in response to AndreasBlack

As you know a Fusion drive consists of a single HDD & a single SSD. If you erase only one of them, you will effectively "break" the Fusion drive and will have to rebuild it again.

Unless you really want to use a Fusion drive, then that would not be a big deal and you can use them as separate drives. Of course, you would lose the performance gain that the Fusion drive would provide.

The fact that you cannot erase the Fusion drive may indicate that the original owner had encrypted the drive via FileVault ... and should that be the case, you would have to know the FileVault password to de-encrypt it.

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Answer 4

AndreasBlack Author

Level 1

5 points

Jul 12, 2023 2:32 PM in response to Tesserax

So if I was just to format/erase Macintosh HD and then attempt to reinstall macOS in it, would that work? or would that break the Fusion?

-Fusion Drive

|_ Container Disk

|_ Macintosh HD <---- This is the Macintosh HD I'm referring to

And on a separate scenario:

If there was no Fusion Drive and the storage of the iMac was comprised of an SSD and an HDD (separated, not "fused") then in order to factory reset the computer: should I just erase both drives and then select one of them to reinstall macOS into?

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Answer 5

Aug 6, 2023 11:49 PM in response to Tesserax

I've got this very same problem. The real deal is the Fusion Drive itself cannot be eased. The "erase" option is disabled. It only reactivates whenever you choose any of the other two, container disk or Macintosh HD. But if you choose the top most "Fusion Drive", the erase button deactivates itself.

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