Remains of Fusion Drive Left Behind...?

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Remains of Fusion Drive Left Behind...?

I recently replaced the 1TB Fusion Drive in my Late 2015 21.5" iMac with a 2TB SSD. It works great, but I've just noticed in Disk Utility that the 24GB SSD portion of the old Fusion Drive is still showing up. I'd assumed the SSD part would be a chip inside the regular spinning platter hard drive case that I removed, but it seems not.

It's only 24GB so not huge, but my question is, as it's in there, can I use it?

I've tried mounting it but I get a "Disk Management Dissenter Error 119930868". I'm guessing I can just reformat it, but I'm nervous to try in case it has somehow tied itself to the new 2TB SSD or does some other unexpected thing that brings the whole system crashing down. MacOS is Catalina.

Thanks in advance for any thoughts or advice.

:)

iMac 21.5″

Posted on May 3, 2023 7:45 AM

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Answer 1

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den.thed

Level 10

82,528 points

May 3, 2023 8:00 AM in response to Sabersense

A Fusion Drive is made up of two drives. (small SSD and large HDD)

If you did not Refuse the drives, as per > How to fix a split Fusion Drive - Apple Support

Then they are just two separate drives in the same box and you should have no problem erasing and reformatting the remaining smaller SSD.

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Answer 2

den.thed

Level 10

82,528 points

May 3, 2023 9:14 AM in response to Sabersense

You're welcome.

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Answer 3

Jan 3, 2024 1:57 AM in response to Sabersense

I've got a similar issue but slight difference. I had a failing fusion drive (the internal SSD part). I replaced the internal HDD with a SSD and used that as the boot drive. However, the broken old SSD fragment still shows up in disk utility but cannot be formatted. Every 15 mins the machine rebooted as it's running some check clearly on the fusion drive and fails.

I can stop it by logging in as admin and using diskutil to unmount the fragment. This seems to stick until the mwc is turned off and then it returns. Is there a more permanent way I can prevent needing to do this after each startup?

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