Multiple disks after installing Catalina?

Hello, drbabbers.

There is no real problem with the volumes configuration here.

What you see is a normal by-product of the Apple's new APFS format. Two volumes are default on the Mac. They are "Macintosh HD" and "Macintosh HD - Data".

The fix for you here is simple and can be done in Disk Utility while you're normally logged into your user account.

• Right-click the volume "Macintosh HD - Data" and Rename it simply "Macintosh HD."

• Right-click the volume "Macintosh HD - Data - Data" and Rename it simply "Macintosh HD - Data"

• Right-click the volume "Update" and Delete APFS Volume...

That's all you need do. It will leave everything untouched on your two critical volumes and you'll be rid of the empty third APFS volume.

EDIT - You might have to unmount the volume "Update" before you can delete it, but I don't think so.

When downgrading from Big Sur to Catalina you need to first of all erase the Disk.

It looks like you did not do this properly.

Boot to your Recovery HD.

Open Disk Utility.

Click View in the menubar and select Show All Devices.

Now you will see the Disk with the Volumes indented underneath.

Highlight the Disk, usually called Apple SSD.... or similar.

Do not select any Container Disk or Volume (Macintosh HD, Macintosh HD- Data or other).

Click Erase.

Give the Disk a name.

Format: APFS

Scheme: GUID Partition Map.

Click Erase.

When Done quit Disk Utility.

Now reinstall Catalina.

The above procedure will erase any and all data on theDisk and its Volumes so make a back up before hand.

When ready only restore your personal data from the backup you made earlier.

There is nothing wrong.

Catalina and Big Sur separate the system from user data.

If you name your drive "Bananas", macOS will automatically create two volumes, "Bananas" and "Bananas - Data".

It so happens that you named your drive "Macintosh HD - Data", now guess what....

If you just rename the drive in the Finder, say to "Oranges" you will see that you will have er... I think you got it.

Follow up -

To be clear, the macOS software lives on the volume "Macintosh HD". It is a protected, read-only volume. Secure.

All of your User data files and info live on the volume "Macintosh HD - Data". You are normally free to access and arrange files there at will, assuming user ownership and permissions aren't violated.

Thank you for this much appreciated. I have followed your instructions and I can't erase the disk itself at the top level. I only have the option to erase on the container disk and volumes. Any ideas?

You don’t really need to do anything. However, you could remove the update volume and you could rename Macintosh HD – Data, as mentioned. To remove the Update volume, select it in Disk Utility and click the remove volume button (–).

You can rename the drive in Disk Utility or in Finder.

Are you trying to compare apples to oranges? 🤣

Are you booted up to your recovery HD.

LOOOL, Old Toad!