Creating APFS fusion drive / conversion to APFS from HFS+ fusion drive fails – “you are trying to create an upside down Fusion”

apfscatalinafusion-drive

I have 1TB Internal SSD and 512GB SD card in a SD slot.

I can create a fusion drive in HFS+ format, and the drive was running fine on my previous El Capitan system. Now that I upgraded my system to Catalina, I wanted to format this fusion drive volume in APFS (currently running Catalina from external hard disk drive, not this fusion drive). But the conversion always fails with either of these 2 error messages:

1:----------------------------------
A problem occurred during conversion from HFS to APFS
APFS Converter exit code is 1
Aborted conversion in commit mode so will restore type
Setting type of disk0s2 to CS
Changing the physical disk partition type in shared mode
Partition modification attempt count was 1
Setting type of disk4s2 to CS
Changing the physical disk partition type in shared mode
Partition modification attempt count was 1
Not mounting APFS Volume
Exiting conversion operations with error code -69860
Error: -69860: The underlying task reported failure on exit

and

2:---------------------------------
It looks like you are trying to create an upside down Fusion:
Main tier (988 GB) is larger than Tier2 (462 GB)

I have no clue about the error message 1, but assuming from the error message 2, APFS fusion drive can not be created if the main drive ( SSD ) is larger than the secondary one? If so, is there a way to force it to make the fusion drive anyway?

what I did to convert:

  1. diskutil apfs convert disk1
  2. diskutil apfs createContainer disk1 disk2
  3. from Disk Utility's Edit menu: "Convert to APFS" ( unmounted the target volume first too )
  4. used a Carbon Copy Cloner and cloned Catalina's bootable volume on external hard disk to the target fusion drive
  5. from OSX Catalina Install Disc

I'm really stuck now. Is there anything else I can try? I appreciate your help, thanks…!

Best Answer

I finally took the plunge and upgraded my iMac to Catalina. It originally had the fusion drive with SSD and spinning hard drive. However, I upgraded the HDD to a Samsung SSD and combined it with the original SSD to create one large CoreStorage logical volume (can’t call it “Fusion” anymore.”)

While trying to convert this logical volume, I ran into all of the same issues you did, so I was able to replicate the problem. However, after about an hour of throwing to force things, I found the trick: reverse the order of the drives

What you think it should be:

$ diskutil APFS create disk0 disk1 “MyVolume”

Reverse the disk identifiers to make it work

$ diskutil APFS create disk1 disk0 “MyVolume”

(I’ll post all of the command output shortly...I’m posting from my iPad as Catalina installs onto a APFS “Fusion” drive).

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