Bootcamp Mess Help

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Level 1

8 points

Bootcamp Mess Help

I'm sorry for the huge message but I want to cover everything; I am wondering if anybody can assist with my fusion drive partition/bootcamp issue please.

I will explain via a sequence of events. I decided I wanted to split my 1TB fusion drive drive on my 2015 iMac and allocate 228GB to Windows 10 and the rest to Mac OS Big Sur; I'm relatively tech savvy so easy enough, or so I thought:

I downloaded 64-bit W10.iso from Microsoft.
I opened Bootcamp Assistant.
I decided storage allocation and highlighted the W10.iso file then pressed continue.
Mac restarted and it auto-chose the disk partition Bootcamp to run the install.
Windows OS installs without issue. Installed drivers and used applications in Windows; all good.

This is where the initial problem began...

Next day I try and option load into Mac OS and the only option is Windows OS.
I load up recovery mode and my original partition is gone.

I honestly don't know what happened. The only thing I can think is that I accidentally split my fusion drive or there was an error from my root cause analysis.

I'm a bit annoyed but not a massive deal; all my important data in iCloud, I have iPad/iPhone etc. so no worries I can wipe it and start again.
I load terminal in recovery mode and run the following command:

diskutil list

I get the identifier names of the physical drives to run the next command:

diskutil cs create Macintosh\ HD disk1 disk2

I get the logical volume group ID and run this command:

diskutil cs createVolume logicalvolumegroup jhfs+ Macintosh\ HD 100%

This worked fine. It seemed to merge my fusion drive back together again.
I install El Capital from recovery, upgrade to Big Sur upon access.
Now I want to split my fusion drive again but it blocks and won't let me continue when I've run Bootcamp assistant and it attempts to choose the drive to install W10, and now I'm stuck!

I know nothing about synthesized drives and I don't want to break my fusion drive but I would like to continue with an install of Mac and Windows OS running side by side via Bootcamp. This is my current situation and specifications:

iMac 27″, macOS 11.0

Posted on Nov 16, 2020 7:42 AM

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Answer 1

Best reply

arrontdep Author

Level 1

8 points

Nov 16, 2020 12:44 PM in response to Loner T

Thanks for your help but I’ve figured out a solution. I had to reboot and do a PRAM reset by holding command & option & r & p. Open up Bootcamp assistant and install normally. Wait for it to reboot and show Windows installer. Click format (I tried this the standard way but didn’t work) the window refreshed, reselect the same partition (it looked blank because it lost Bootcamp name but the storage was correct) and this allowed me to get past that wall where it was stuck.

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Answer 2

Loner T

Level 9

59,471 points

Nov 16, 2020 9:02 AM in response to arrontdep

Post the output of

diskutil apfs list

If the Fusion drive is incorrectly built with the CS commands and the 'faster' disk as secondary, you will run into issues. The CoresStorage (cs) commands are a bit different from the corresponding APFS commands. APFS checks if the build uses the larger disk drive as secondary, while CS does not.

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Answer 3

arrontdep Author

Level 1

8 points

Nov 16, 2020 9:28 AM in response to Loner T

Bootcamp works to the point that it loads the .iso and reboots but then when I try and choose the Bootcamp disk image to install Windows 10 onto an error appears something like we couldn't create a new partition or locate an existing one and won't let me click next.

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