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Disk Partition Map

I see there are only three disk partitions in my SATA HDD. Why are there two more disk partitions shown in the disk utility? Meanwhile, when I was trying to do Time Machine backup, there is an error message shown as the attached text. I just reinstalled macOS Catalina 10.15.2 on this iMac from the Internet and I erased the disks beforehand. Would this even be possibly caused by some malware from such fresh clean reinstallation?



iMac Line (2012 and Later)

Posted on Jan 14, 2020 7:55 PM

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Question marked as Top-ranking reply

Posted on Jan 14, 2020 8:43 PM

Although I am unable to read your screenshots (too small for my eyes, LOL), I am assuming that something went awry during your erase/reinstall process or you didn't pick the right one to erase. Catalina creates two volumes by default: Mac HD (read only/system volume) and Mac HD - Data (read/write containing your apps, user folder, etc). And, when you erase/reinstall, Catalina will - every time - create another Mac HD Data volume unless you follow the steps exactly. You can also do a search here for Mac HD Data and find some other threads with things people have done to get rid of the second one.


https://support.apple.com/en-us/HT208496

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Question marked as Top-ranking reply

Jan 14, 2020 8:43 PM in response to Merslamarer

Although I am unable to read your screenshots (too small for my eyes, LOL), I am assuming that something went awry during your erase/reinstall process or you didn't pick the right one to erase. Catalina creates two volumes by default: Mac HD (read only/system volume) and Mac HD - Data (read/write containing your apps, user folder, etc). And, when you erase/reinstall, Catalina will - every time - create another Mac HD Data volume unless you follow the steps exactly. You can also do a search here for Mac HD Data and find some other threads with things people have done to get rid of the second one.


https://support.apple.com/en-us/HT208496

Jan 14, 2020 8:15 PM in response to Merslamarer

It would appear that you have created two iMacOS - Data volumes, an iMacOS volume, a Mac volume, and an Apple volume. What did you do? Why are you formatting a HDD using APFS? You should have used HFS+. APFS is intended to SSDs.


Exactly how do you want this drive configured? You will need to erase it and start over.


Install El Capitan or Later from Scratch


  1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
  2. Select Disk Utility from the Utility Menu and click on the Continue button.
  3. When Disk Utility loads select the drive (out-dented entry, usually model info and size) from the Device list.
  4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
  5. Set the Format type to Mac OS Extended (Journaled.)
  6. Click on the Apply button, then wait for the Done button to activate and click on it.
  7. Quit Disk Utility and return to the Utility Menu.
  8. Select Install OS X and click on the Continue button.


This should install the current version of macOS - Catalina. You can configure the other two volumes afterward or you can do it before installing macOS while still in Disk Utility.

Disk Partition Map

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