I am wanting to reinstall Catalina onto my iMac as a fresh copy (reformat and delete all data). Because my iMac is a fusion drive, do I just install onto the Macintosh HD drive? Or do I need to specify the location of the fusion drive. Or does the installer just 'know' where this is?
Sorry for the (maybe) confusing question. I just wanted to check before going ahead with wiping everything and reinstalling.
You should use Recovery Mode to both completely erase, and then, install a "clean" copy of macOS Catalina.
Ref: How to reinstall macOS from macOS Recovery - Apple Support
Disk Utility should show an "Fusion Drive in the left pane. You should be erasing the "Fusion Drive". If you don't see the Fusion Drive, then click on "VIew" within Disk Utility and select "Show All Devices" so that the physical drives appear in the left pane of Disk Utility. This setting may also allow you to see the Fusion Drive. This is a very annoying change in Disk Utility. You want to erase the "Fusion Drive" item.
First, I'm assuming that your iMac came with macOS Catalina installed ... is that correct? ... or was it upgraded from an earlier version of macOS? Regardless, the Finder app should "see" your Fusion drive as a "single" drive. Does it?
Yes. It shows the tree: Fusion Drive - Contain disk2 - Macintosh HD.
So I will reformat from the Fusion Drive level.
And I am assuming from here that once the OS has reinstalled, the Fusion Drive will work as it did previously (by allocating common applications/tasks etc to the 128Gb SSD).
Thanks. So just to double check again, on a Fusion drive it doesn't matter where I specify the install?
Yes.
Reinstalling Catalina from scratch - onto a 2TB fusion drive
