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ern-o Author

Level 1

4 points

Intel Mac Fusion Drive Erase and reinstall Mac OS

I have an older Mac that I wanted to send back to apple. I am trying to erase the drive and re-install Catalina. I have done this several times using Disk utility. The process seems to be successful but when I go through the set up and check About this Mac>Storage there is now another hard drive. I think the original computer had a Macintosh HD and Macintosh HD - Data. Somehow a Macintosh HD-Data-data was added. Since then I tried to erase and remove all the volumes shown in Disk utility and now am unable to install Catalina on AFPS since it is unable to add a Pre-boot volume.

My main question is, Did I actually erase the drive already? I was concerned since the new volume that showed up had "other volumes" with varying amounts of data that would change when I would try to delete and reinstall the OS. I only wanted to install Catalina so that the imac was working and I could get the $75 the computer is worth on trade in. I would rather forfeit the 75 and ensure the mac is clean of data. I know I made a mess of this on my own but I do appreciate any thoughts.

Posted on Mar 2, 2023 10:23 AM

Top-ranking reply

HWTech

Level 9

60,284 points

Posted on Mar 2, 2023 11:07 AM

With an Intel Mac you want to erase the whole Fusion Drive item. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives, hidden Containers, and perhaps even the "Fusion Drive" object appears on the left pane of Disk Utility.

Select the "Fusion Drive" item and erase it as GUID partition and APFS (top option) if installing macOS 10.13+, otherwise erase it as GUID partition and MacOS Extended (Journaled).

Since there are now two "Data" volumes, this means all of your data still exists on the original "Data" volume.

When using a hard drive, it is still possible to access data using data recovery apps unless the hard drive is encrypted or zeroed out. I'm not sure if it is possible to encrypt the original "Data" volume now or how to go about it since the original "Data" volume is no longer a part of your current macOS installation. It may be possible to break the Fusion Drive setup, then use Disk Utility to secure erase the hard drive (no need to do this with the SSD) which requires accessing the "Advanced" or "Options" button on the Disk Utility "erase" tab (I didn't think this was still available, but a co-worker was just doing this secure erase to an external hard drive the other day). After a single pass of zeroes, then you need to recreate the Fusion Drive and reinstall macOS. I recommend making & using a bootable macOS USB installer in case Internet Recovery Mode has issues.

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Intel Mac Fusion Drive Erase and reinstall Mac OS

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