psymac

macrumors 6502a
Original poster
Jul 17, 2002
527
128
Hi all,

Attempting to split my 2TB iMac 2017 27" iMac Fusion Drive to use the SSD and HD separately. Have followed the instructions, but am getting "Unable to unmount drive" error. Do I have to boot from an external drive in order to do this? The instructions I'm using don't note this, so not sure, thinking now I can't unmount a drive that I boot from.

https://www.lifewire.com/split-fusion-drive-apart-2260166
[doublepost=1512661199][/doublepost]Ok, my bad, that Lifewire is not the best for instructions, the Macworld article is better, and does note I have to boot from Recovery mode as I suspected.
 

Fishrrman

macrumors Core
Feb 20, 2009
22,218
8,266
"Do I have to boot from an external drive in order to do this?"

Yes.
I may be wrong, but I don't believe this can be done from the recovery partition -- because "the split" will wipe out the recovery partition along with everything else.

Either boot from an external (bootable) drive, or perhaps you could create a bootable USB flash drive and boot from that, then go to terminal to split the drive...
 

psymac

macrumors 6502a
Original poster
Jul 17, 2002
527
128
Actually it did work from Recovery mode, I assume its getting the OS from the internet. Still thinking however Apple didn't put the faster SSD blades in the 2TB Fusion Drive, as I'm getting 'only' 750/2300mb/s R/W speeds for the 128GB SSD.
 
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