Thank you but does anyone know how to do a clean install on a Fusion Drive?
@ToddJ
You did not specify model of the machine you own. If it is a laptop, I strongly suggest to invest in an SSD; you will see performance degradation otherwise (in comparison to those who do have SSD). The other item I would recommend is maximizing RAM.
Installing OS on a fusion drive is in no way different than doing so on an SSD.
If you want to erase your drive completely (you will
loose all the data on that drive) and install completely fresh system, boot into
recovery, then use disk utility to erase your drive. Once that is completed, use same
recovery menu to re-install Mac OS. Please be aware that only the Mac OS (which can run natively on your machine) will be installed with that procedure. If your machine is compatible with Big Sur, than Big Sur (latest official release) will be installed on your "clean" drive. Thereafter, you can use Migration Assistant to move your data back from a backup ( A disclaimer: I never had to use Migration Assistant)
A less destructive way to reinstall OS, involves booting into recovery and simply choosing "re-install Mac OS" from
disk recovery menu. Under normal circumstances, operating system will be reinstalled (latest compatible version) without erasing other data on your disk. However, there is never any guarantee of total success, therefore you
should always have a recent verified backup.
One other necessary precaution is to check your drive thoroughly with disk utility to assure it is in good working order, and not about to fail.
Please follow the attached link, and do read Apple's official instructions:
https://support.apple.com/en-us/HT204904 (click on the link, or copy and paste link into your browser) It's only one page and very clear.
Hope this may be of same Help
27 inch iMac 13,2 with 1 TB Fusion Drive , 24 GB RAM, 3.4 GHz Quad-Core Intel Core i7, Big Sur 11.5 beta1