Reformatting Fusion drive with Catalina

Hi everyone!

I’m turning to you for help again.

I have just purchased a 2013 iMac with fusion drive. It has a nice clean Catalina install, but I would still feel better if I could reformat the disk and erase everything.

However, I have no experience with fusion drives or with Catalina, so I was a bit taken aback with what I saw when rebooting in recovery mode.

Am I supposed to delete both the regular and the data partition? Will the drive still be “fused” after that and I can just do a clean install then? I want to make sure I do not do anything stupid. I now have a perfectly functional computer, but I feel uncomfortable using it without having wiped it first.

I’ve tried reading up on how to proceed, but I’m actually a bit confused. Is there anyone here who has done what I am trying to do?

Thanks a lot!

AFAIK you should treat the Fusion drive like any other drive. Or, better yet, yank it out and replace it with a SDD.

I agree with the SSD. However, I bought this with a very limited and specific purpose, namely to play fitness videos in my tiny fitness corner, so even if the HDD were to die it wouldn’t be the end of the world. I liked the screen (the whole thing is in near pristine state) and the large disk is good to store the videos. SSD versions were more limited on that front and I did not want to spend much given the use scenario.

If anybody has a more specific guideline on what to do with the disk that would be great!
I might even split the drive, so that I can still access the system if the HDD goes.

Have you thought about going this route – leaving the iMac intact but booting from an external modern ssd drive? 2017 27" iMac: More memory vs. external boot SSD? - Hardware - MPU Talk

A DDG search for “split fusion drive” returns several hits on how to split or unsplit a fusion drive.

I’ve done this on an iMac with a fusion drive running High Sierra, not Catalina, so perhaps this isn’t helpful…
I proceeded as @jec0047 suggests: as normal. I also goofed around in Terminal and purposefully unfused and re-fused the fusion drive. It wasn’t hard to do. Apple has step-by-step instructions.

What size hard drive? The 1tb version has a pathetic SSD (24 or 32gb) while the 2 and 3 has a 128gb SSD. For your use case the fusion drive perform adequately. On recent MacOS versions the volume is split into a system container and a data container. You can reinstall the system without affecting the data container.

If you want a fresh, clean install just erase everything and install.

It’s 3,2 TB.

Going the Terminal way scares me, because it deletes the recovery partition too (if I understand correctly). Basically I would like to erase the drive just to be absolutely certain that there aren’t any virus/adware leftovers.

I think I would leave the fusion drive alone for the moment, if it ever dies I’ll worry about it then.

So the real question would be: do I delete the whole container (system and data) or what do I do?

True. But I was a bit wary, since I’ve never done it and didn’t want to brick the computer.

I suppose I’m just uncomfortable with new experiences (fusion drive and a system with a different architecture - I’m still a High Sierra person).

Thanks for the tip, but I think it doesn’t apply to my user case.
My major concern is having a clean drive; only secondarily am I worried about the HDD crashing.

I was thinking aloud a bit I guess.