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I mistakenly used Disk Utility to remove a Bootcamp partition, which has left a ‘ghost’ disk (showing as physical & internal) of 128GB that I can’t seem to remove.

I have wiped the SSD and reinstalled macOS, but the disk is still there. Could someone help me merge the 128GB disk with my 1TB SSD?

Attached are some screen shots:

Mac SSD

Unwanted disk/partition left over from removing the Bootcamp partition

Terminal output from diskutil list and diskutil cs list

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  • What is the model and year of your Mac. I ask because diskutil list shows two internal drives which is unusual for a Mac when the larger of the two is a SSD. Commented Sep 15, 2022 at 6:24
  • Hey David, thanks for your reply. It's a iMac (Retina 5K, 27-inch, 2019) with a single 1TB SSD. The Untitled internal 128GB flash storage only appeared after I had removed the Bootcamp partition (also of 128GB) from the internal SSD using Disk Utility
    – Joss1992
    Commented Sep 15, 2022 at 6:37
  • The problem is you posted the output from diskutil list which shows two internal drives. You state in your previous comment the Mac has a single single 1TB SSD. What does the output from diskutil info disk1 | grep -e Protocol -e Solid show? Commented Sep 15, 2022 at 7:23
  • Yes it's weird isn't it! Here's the output: Protocol: SATA Solid State: Yes
    – Joss1992
    Commented Sep 15, 2022 at 7:36
  • Ok, then what does diskutil info disk0 | grep -e Protocol -e Solid show? I would assume Protocol: PCI-Express Solid State: Yes Commented Sep 15, 2022 at 7:44

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Your Mac has two internal SSDs. Normally, Apple did not sell the 27-inch 2019 iMac configured this way. Any SATA drive provided by Apple is normally a HDD because the 6 Gb/s SATA interface is faster than Apple HDDs, which do not exceed 3 Gb/s. All SDDs from Apple for the 27-inch 2019 iMac use the faster PCI-Express. If one wished to have a 1 TB SSD, then Apple would sell the Mac with PCI-Express 1 TB SSD. The 1 TB drive would not be SATA. In such a case, there would be no SATA drive installed.

You could merge the two drives by creating a Fusion drive. You probably want to have a Fusion drive since the smaller SSD is significantly faster than the larger SSD. In other words, the larger drive is limited by being legacy 6 Gb/s SATA drive. The smaller drive is a PCI-Express drive which does not have a 6 Gb/s limitation

You could try using the command diskutil resetFusion to create the Fusion drive. See the Apple website How to fix a split Fusion Drive for further instructions. You may have problems using the instructions because the larger drives is a SSD and not a HDD. If so, I can post other commands to create the Fusion Drive.


Alternate Possible Configuration

Instead of creating a Fusion drive, this configuration would put macOS on the faster drive and the users' data on the slower drive.

You could erase the smaller faster PCI-Express SDD and install macOS there. You can then set the home directory for each account to be on the larger slower SATA SDD. To do this, first goto the User & Groups pain of system preferences. Next, select Advanced Options... for a user, as shown below.

Finally, change the home directory to be on the larger slower SATA SDD, as shown below.

I should also point out you would get significantly greater performance by add a Thunderbolt 3 external SDD, which be slightly slower that the smaller internal and exceptionally faster then the larger internal drive. You could use the larger internal drive for archiving and backups. You also would be able to instal Windows 10 on this external drive.

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  • I had no idea my mac had 2 internal SSD's!? I configured it when I bought it to have a single 1TB SSD and the other one has never been accessible or visible. Okay thank you, I will try the fusion drive tutorial you linked and report back with how I get on.
    – Joss1992
    Commented Sep 15, 2022 at 8:42
  • Does making a Fusion Drive from 2 SSDs confer any benefits to a user over using the smaller drive for the OS and applications only, and the larger one for everything else? I know this isn’t what @Joss1992 asked for but my (brief) web search on using 2 SSDs for a Fusion Drive seems to indicate that it isn’t recommended. Commented Sep 15, 2022 at 16:52
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    That’s not reasonable, I would say. What's much more likely is that there are two partitions, one is the space that had originally been partitioned off for BootCamp, and the other partition has the APFS container. When the OP erased the SSD, he did not actually erase the SSD, he erased the APFS container. Commented Sep 15, 2022 at 20:15
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    @RusticChevalier, you do not use symlinks. See my updated answer. Commented Sep 15, 2022 at 21:55
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    @RusticChevalier: If both SSDs had similar access times, then I would not recommend creating a Fusion drive. In this case however, there is a significant difference in access times between the PCI-Express SSD and the SATA SSD. The whole reason Apple included space for both a PCI-Express drive and a SATA drive was to allow for a Fusion arrangement. Although, Apple did intend for the SATA drive to be a HDD. The OP should be able to create a Fusion drive from the two internal SSDs. If there is a problem with the result, the OP could then try a different non-Fusion configuration. Commented Sep 16, 2022 at 5:24

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