OS Catalina. 2 MAC HD data drives

To remove the redundant “Macintosh HD data” before a fresh Catalina install:

In recovery mode disk utility there is the VOLUME + - in the top of the box. Select your “Macintosh HD data” and then click -

This will delete it.

I just had this happen to me after I had problems with an update in Catalina which caused it not to boot up, so I had to erase all my data and do full reinstall of Cataline then a full data restore from Time Machine.

Apple Support guided me through the process.

1. Back up the system on Time Machine (Full back up or do a new incremental before starting)
2. Remove/unplug any devices (including Time Machine connections) and any other external drives.
3. Reboot Machine and ensure only Finder is running.
4. Open Disk Utility
5. One of the Macintosh HD - Data will have the Home icon, one will not, it will also be the one with the lowest usage used about 1mb/2mb.
6. Select that and use the - (minus) key at the top, this will remove the Partition/Disk Image (Note: Erase will not do the job as this will just remove the data on the drive), you will be prompted to remove it. Confirm it.
7. Reboot again.
8. Check to ensure the new HD Data, now correctly shows the Free Space and Used Spaced which when added together match the max capacity of the volume (unless you have other partitiions defined).
9. Plug in again all external devices - Time Machine drive etc.
10. Do another backup / incremental after.

I had this after doing a recovery. Here's how I fixed it, WITHOUT going into recovery mode (although that is the proper way to do this):

1. I ejected the "iMac HD - Data" that had mysteriously appeared right below my HD icon;
2. I opened Disk Utility from the Utilities folder;
3. I saw the 2nd "iMac HD - Data" volume had been dimmed;
4. I saw I could click the - from the top menu to delete the volume.

Note that before I tried this, I just ejected the volume and emptied the trash thinking it would work like the old .dmg install mounts, but upon restarting lo and behold there it appeared.

Hope that helped give an easy way to end the suffering!

Chris.

The -Data drive/volume is your working volume with your applications, home folder with its sub folders, etc. The other drive/volume is a read-only drive for the system and its files. It's Apple's next step in securing the system from outside miscreants.

I've rename named my volumes. The data volume is Toad Hall and the other is Catalina:

Just ignore the non-data volume.

This illustrates my case.

From the reply by craig150 it seems it happened when I downloaded Catalina from the Mac App Store to create a backup bootable USB installation drive. It looks like the data volume being used is the one at the bottom, but no idea what to do to revert to normal, other than re-formatting the HD again.

Forcing us to live with apples so called security scheme of making 2 partitions on my drive is crap! Guess I won't be upgrading to Catalina any time soon. As soon as I saw my test drive was formatted this way I knew I wasn't going to like the direction they're going in. Too bad since I've been an Apple fan and Mac user since about 1986.

I deleted both the Data drives, leaving the HD drive in place. Shut down and restarted in Recovery mode and tried to use Time Machine to recover. It found Time Machine but would not start the download. Then tried to Reinstall Mac OS onto Mac HD. Got the message "The target volume is part of an incomplete system and cannot be installed to".

HELP please

Craig, you are right I missed part 5. Have now connected old time machine and am "hopefully" reinstalling Mojave. If it works I will stay with it for ever. If not I may try again, but I don't remember seeing internet recovery mode as an option. Keeping my fingers crossed.

Just adding that the second data drive on the desk top is the extra. I renamed it so I could tell the difference in disk utility when in recovery mode . I removed it and then restarted. No need to wipe the drive and perform a reinstall of the system.

I have not downloaded Catalina twice. I just bought a brand new computer, and when I try to use time machine, it won't let me. I have the double data hardrive problem. I don't even have one time machine backup to use. Now what? I thought when I bought the new computer all my problems would be over.

Craig150,

I hardly think this issue is solved.

The worst part of this experience for me is that Time Machine was horribly corrupted during the process of restoration or, did not import and parse the data properly. I did end up renaming a data drive to move forward but everything after that was a domino effect of failures.

The double Data drive images caused Time Machine to fail until a drive was renamed.

How is one to know which drive is legitimately connected to the installation and going to function properly? I have moved on and just left things alone as I have spent so much time with this upgrade issue on so many levels that I need to get work done instead of bang my head against the Apple wall. I can only hope Time Machine is functioning properly, I no longer trust the process.

At some point down the road I will wipe everything and start fresh, probably after a few iterations of upgrades, but this has been a ridiculous exercise in Apple dramatically changing the game with no sensible path for educating end users in place.

Very frustrating,

gchdrake