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Ian R. Brown Author

Level 7

22,193 points

Big problem after clean install of Big Sur!

I tried to do a clean install of Big Sur on my Catalina iMac.

I booted up from an external SSD.

There were 2 drives showing in Disk Utility as in the picture below (which is NOT my iMac).

I had no problem erasing Mac HD but Mac HD-Data refused/failed to erase.

So I continued to install Big Sur on my iMac which succeeded except for one thing. . . . although there was no sign of all the data that had been on my Mac, it now appears that I have 2 Mac HD-Data volumes, one with only 4.27GB used and the other with about 349GB used.

All this data should have been erased. There is no sign of it anywhere.

Can you tell me where I went wrong and if possible, how to rectify it?

iMac 27″ 5K, macOS 10.14

Posted on Aug 27, 2021 9:36 AM

Top-ranking reply

samtenor

Level 4

1,756 points

Posted on Aug 27, 2021 10:54 AM

If you want to clean install Big Sur and want to erase the internal drive -- you should erase the "container" to start.

I would suggest to make a USB installation drive first.

By booting directly from USB drive - you can use disk utility to erase the container, name the new volume (such as Macintosh HD alike) and then install the MacOS.

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Big problem after clean install of Big Sur!

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