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amenityelk

macrumors newbie
Original poster
Nov 7, 2020
10
0
NYC
I'm planning on doing an internal upgrade of my late 2014 iMac 5K's Fusion Drive to an SSD (Samsung EVO 860), but I'm installing Big Sur on the SSD externally via a SATA/USB cable first, to make sure everything works before I open the iMac up.

I was totally unable to install Big Sur on the SSD via my iMac—every time it restarted after assembling the components when you first click install, it would just boot onto my internal fusion drive (with Mojave installed), without completing the BS installation. So I installed it on the SSD via my MBP (touch bar, 2016) which already has Big Sur installed internally. That worked fine and I was able to boot from the external on the MBP.

But, I can't boot from the external SSD on my iMac—the drive isn't available from the startup disk selector in System Preferences, nor in the startup drive picker when holding down option as the iMac starts.

I used APFS / GUID partition map on the SSD. I also get an error when plugging it in while booted into Mojave, that says "This disk uses features that are not supported on this version of macOS." I assume that just has to do with it having Big Sur installed, but not sure if that provides any clues...

Anybody have any ideas? I hope that wasn't too convoluted an explanation. Thank you!
 

gilby101

macrumors 68030
Mar 17, 2010
2,921
1,616
Tasmania
I used APFS / GUID partition map on the SSD. I also get an error when plugging it in while booted into Mojave, that says "This disk uses features that are not supported on this version of macOS." I assume that just has to do with it having Big Sur installed, but not sure if that provides any clues...
This is to be expected. BS uses features of APFS that Mojave does not understand.
But, I can't boot from the external SSD on my iMac—the drive isn't available from the startup disk selector in System Preferences, nor in the startup drive picker when holding down option as the iMac starts.
Suggests that there is something incompatible between the 2014 iMac and the SATA/USB cable. Maybe you should specify what 'cable' and perhaps someone else will know the answer to compatibility.
 
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