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Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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What is the best way to wipe a fusion drive before Big Sur install

I’m having issues with machines using fusion drives that have had a Big Sur installation failure. My customers are coming in after they have failed and then attempted all sorts of fixes to get Big Sur to work. I’d like to just clean the whole fusion drive mess up and start off clean. Any expertise on this would help a lot.

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Booting up from an external drive (I’ve been using Mojave and have only done Mojave systems) then within Disk Utility wipe both drives leave the blade SSD alone, repartition and install Big Sur onto the HDD, make sure it boots up and is working correctly.

Now you can re-join the SSD to the HDD into a Fusion Drive set following this guide How to fix a split Fusion Drive

Of course make a backup of anything first thats important.

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