Model A1419 / Late 2013 / 3.2 & 3.4 GHz Core i5 or 3.5 GHz Core i7 Processor, ID iMac14,2

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How do I split Fusion drive on Mojave / APFS?


I have a 2013 iMac that has a Fusion drive. I want to replace its internal HDD with an SSD. My understanding is that I should split the Fusion drive before performing this.

I referred to the article which discusses the use of diskUtil and Core Storage to get the GUIDs and split the drive.

However, invoking disktutil coreStorage list returned ‘No CoreStorage logical volume groups found’. I then tried diskutil list, which returned more information, apparently showing the fused drives as ‘synthesized’. I read a bit about this in other discussions, and it seems like this is perhaps a Mojave/APFS version of a Core Storage Fusion config.

I’m wondering what I need to do to split my Fusion drive. Is there something else to use, or do I not even need to split the HDD/SSD before replacing the HDD?



Update (12/22/2018)

I wonder if I need to downgrade it to High Sierra, and setup the drive as HFS?

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Sadly, Apple has not updated the Core Storage section on the developers web site with Fusion Drive running with Mojave. The Man page doesn't offer any help either.

Yes, you do need to break the Fusion Drive set before altering things otherwise the drives will be confused. In this case you also need to keep in mind you can't run the system with a dual SSD Fusion Drive set it won't really make things faster.

I haven't played with Mojave Fusion Drive setup yet my self so I don't know if Apple has any magic behind the scenes.

FYI - Mojave APFS is different from High Sierra APFS so I doubt down grading would work.

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I did this earlier today on an iMac. Boot to a Mojave USB boot installer. Then Utilities —> Terminal. The commands are along the lines of:

diskutil apfs list

Then make note of the “virtual disk” that is the “Fusion Drive”. This is made up the PCI Flash and the other spinning drive. You can see how the text output of the drive structure is hierarchical.

Let’s say that virtual container disk is identified as “disk0”

diskutil apfs deletecontainer disk0

This command will split your fusion drive, and leave you with two new drives to format via Disk Utility (which you can run in the same USB Booted environment you’re already in).

Format them (the SSD and the other drive) as whatever you want.

I recently did this prior to replacing the slow spinning disk that comprised the 1TB of my Fusion Drive. Replaced that with a 500GB SSD which is SATA3. Installed Mojave onto the 128GB PCI “Blade” Flash and formatted the other SSD.

I then store User home folder on the larger SSD, and macOS and other apps run off the faster PCI-based SSD.

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With this tip, I shared my fusion drive. It's the right decision. thank you!


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I did a similar thing with a Mac Mini. I simply took a time machine backup and then booted to internet recovery. From there I formated each drive in disk utility separatly to break fusion. I then swapped over to the SSD. Worked fine. I hope this makes sense.



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To break the Fusion drive should be quite simple, I believe: Boot the iMac from an Arch Linux installation USB stick, do lsblk to identify the two drives, then do dd if=/dev/urandom of= /dev/<disk> for both disks to erase all information at the beginning of the disks (just write a few MBs), and that should do the job. This procedure of course will erase all data on both drives, so be sure to back up before.

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I’m having this same problem and haven’t found resolution. The system fully shows the Fusion drive as one disk, so I have no way to erase each sub-disk separately in order to split it. Any further advice from any would be greatly appreciated.

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