Two Volumes Named "Macintosh HD - Data" Now Appear in Disk Utility in Addition to "Macintosh HD".

Each time you put a copy of Catalina on it installs another HD Data and may double your other data creating multiple Volumes with the container.

you must erase each HD Data drive in recovery (world spins) then erase the top layer (your physical drive). Then download Catalina in recovery NOT your copy. That is what is creating the multi volumes. Then set up your Mac from your time machine backup

Ok, I did CMD - R and went to disk utilities. Then I went to the second MAC HD-DATA and clicked on it and deleted it. Then I restarted, and now there was only one hard drive, and all looked fine so far. In any case always have a working Back up available in case things are not fine.

MAC HD

MAC HD-DATA

--> MAC HD-DATA

I can't say for sure, but I doubt your fan running has anything to do with this new hard drive structure.

What do you mean by "the same thing" - you are supposed to have two hard drives:

Macintosh HD

Macintosh HD Data

(see https://support.apple.com/en-us/HT210650)

FWIW: I had this structure after upgrading to Catalina

Macintosh HD

Macintosh HD Data

Macintosh HD Data

I removed the last instance of HD Data in Disk Utility (right-click and choose Delete volume), and now things look as they should. And don't worry: you won't be able to delete a drive you're not supposed to delete.

Definitely not supposed to happen - you're only meant to have 1 Macintosh HD and 1 Macintosh HD - Data

I had a tonne of issues ranging from slowness, corruption of certain areas, errors so I ended up just erasing the disk and starting with a clean install - works really well.

Cheers.

Same here: I did a clean install of Catalina, and at first I had two volumes:

[Mac HD]

[Mac HD] - Data

Then I reinstalled my apps and ended up with three volumes (included space used for comparison)

[Mac HD] uses 10.56GB

[Mac HD] - Data uses 515.08GB

[Mac HD] - Data uses 774 KB

I went ahead and removed the third (774KB) volume in Disk Utility. It hasn't come back yet, and so far I haven't noticed any odd behavior.

Appreciate it if anyone could shed some light on this.

To follow up: I have an iMac and a MBP. I did a clean install on both systems — and both exhibit the behavior described above (two HD - Data volumes).

I followed @Brallen01's tip and got... nothing (see screenshot); no vol identified (note also: Forklift does NOT show the rogue second data volume).

For completeness, the third-party apps I installed are:

A Better Finder Rename

Bartender

Default Folder X

Dropzone

Little Snitch

LaunchBar

Lyn

Marked2

Microsoft Office 365

Omnigraffle

Printopia

Scrivener

Studiometry

Typinator

As I did on my iMac — I'm going to delete the second volume, and see what happens :)

I had the same issue as well. I saw this after going back to Mojave (via TM) to update some iPhoto-to-Photos files. I rebooted via option-command-R (Restore), and used TM to go back to Catalina. I found this (via Disk Utility)...

Seeing this as an error I then did a restore using the same option-command-R, but asking for Catalina. Now, I have 2 Data drives. I took snapshots of all 3. Note that I somehow have 6 volumes!

Can someone help?!?

Bizarre, I'd give it another go but when you're erasing the disk, make sure you select "Show all devices" from the "View" option. and then erase the whole hard drive, not just a volume.

If it does it again, try internet recovery, not a normal recovery as this will download the OS from the internet and not use your recovery partition.

Very strange then! possibly a bug if it appeared from a clean install - I haven't had it happen to me yet.

If it does, right click on that volume and click on "show in finder" will be interested to see where the new phantom one is pointing to.

Must be a bug that is creating it then at some point in your workflow - maybe its a certain app you're installing that triggers it. and if it contains nothing I would just delete it.

if you do Shift + Command + period (reveals hidden files) does it show anything that looks important?

I also did a clean install and ended up with two hard drives. The second MAC HD-DATA can actually be erased, the first one not. To back up I unmounted that disk. Definitely that is some problem with Catalina, and I am also interested how to resolve this.

I boot into Mojave and launch Disk Utility. Then to Containers and select the destination drive to use the minus on that data drive and the read only drive that use to be Catalina. then proceed with the Catalina install after creating using the plus sign on that container. Case closed no more dups.

Hi,

After trying different ideas, the one that worked for me, which was simple, was to just rename the smaller of the two duplicate hard drives another name. Someone earlier mentioned ghost so that is what I named it. Then I opened time machine preferences and chose the real hard drive to back up. No problems since. So thank you, ghost writer.