What is the Macintosh HD Data volume doing on my hard drive?

As of macOS 10.15 Catalina with the APFS file system, the hard disk of the Apple Mac is divided into “Macintosh HD” and “Macintosh HD data” by default. The two volumes have different properties that are unlikely to be immediately apparent without further insight into the matter. Therefore, in this guide you will find everything you need to know about the second volume, its tasks and how to deal with both parts of the hard drive. Do you have any questions or comments? Then leave a comment! Are you struggling with the 2019 Mac OS? Then take a look in this blog post.

What is the Macintosh HD data volume? Why does it show up in Disk Utility but not in Finder? And why can't you delete it? Here you can find all information on the topic.

What is the Macintosh HD data volume? Why does it show up in Disk Utility but not in Finder? And why can't you delete it? Here you can find all information on the topic.

What is “Macintosh HD Data”?

If you upgrade your Mac to macOS Catalina (or Big Sur in the future), you will find the Macintosh HD data volume in Disk Utility in addition to the well-known Macintosh HD as the system disk. The latter is the volume on which you can make changes, write, read and delete data and house third-party apps and data. Apple programs such as Safari, Pages or Numbers, so that they can be adjusted via update or by users.

The whole thing is separated from the aforementioned and well-known “Macintosh HD”, which serves as the system volume and contains the system files, scripts and the like for macOS. The separation serves to secure the system data so that it is not compromised - neither intentionally nor accidentally. Or as it is at Apple in the Support document on the subject means: "macOS Catalina is running on a read-only system volume [...] This volume is completely separated from all other data to prevent accidental overwriting of critical operating system files."

The new volume says, among other things: "When upgrading to Catalina, a second volume will be created and some files may be moved to a folder called 'Reassigned Items' [...] Your files and data will be on [...] 'Macintosh HD - Data' saved. Both volumes are shown as "Macintosh HD" in the Finder“- Data was transferred to data in the German version of the operating system. And on the so-called volume, as already described by Apple, there may be a folder with a collection of moved files and apps.

What is the "Newly assigned objects" folder used for?

The two volumes will be displayed in the disk utility. In the Finder, they are combined into one element, the well-known Macintosh HD. If you look through the hard drive in the Finder on your Mac, you might notice the “Newly assigned objects” folder. This has already been described above. But what does it actually contain? Well, according to Apple, the files and folders that can be changed or created by the user themselves will be moved there that were previously (under macOS 10.14 or older) in system folders. 

From macOS 10.15 Catalina - and from autumn 2020 also under macOS 11.0 Big Sur - the system folders will be cleared out if you upgrade from macOS 10.14 Mojave or older. Anything that does not belong to the write-protected operating system is packed in a box like when moving and is no longer placed in the work room, but in the hobby room in the new house. Whether you unpack them there, sort them out or decide to delete the new folder completely, that's up to you.

Conclusion on the new volume from macOS Catalina 

The topic is of course not that new; after all, you can equip your Mac, iMac or MacBook with the current system since autumn 2019. And also the new system for 2020/2021 has been for a long time known. Nevertheless, it is important to know what is going on on the Mac, what the individual APFS volumes mean in the hard disk service program, and that you cannot delete the “Macintosh HD data”. It is precisely the changeable and adaptable part of your Mac that has been stored separately from the secured system. You can find more information, details, instructions and advisory content with this post.

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  1. Alfred Sassenfeld says:

    Hi Jens,
    I am interested in the antivirus app Malwarebytes to install on my Mac with Catalina. Is there also a German version and if so, where can I download it. Is that freeware?
    Thanks in advance,
    With kind regards,

    • sir appleot says:

      Hello Alfred! Malwarebytes is unfortunately not freeware and has to be paid for. You can do it here via my tracking link to Malwarebytes (then I get a few cents when buying, which helps me to run the blog). When I go to the website, it is already in German. I am assuming that the software will then also be in German. But there is a free trial version that you can download. Then you can see whether it is really available in German.

  2. Antonia says:

    The concept is not bad in itself. Unfortunately, only the implementation is the total botch. Instead of overlaying the volumes completely opaque, the system volume could have simply been mounted in the "/ System" directory, and that would have been good. / usr, / bin and / lib could have been symlinked there.

    • Jen Kleinholz says:

      Hi Antonia! I'm not well enough in the matter to criticize Apple. But I suppose their programmers thought about the topic for a few minutes before they started implementing it. Still, maybe you're right and it would have been so easy and more practical. : D

  3. SoHo says:

    I have a question on this topic :)

    I work with a MacBook Pro (Retina, 13-inch, Late 2013) with macOS Catalina (version 10.15.7) and want to update to BigSur.

    During the installation I now have the choice to install Macintosh HD or Macintosh HD data on the volume. I didn't dare to "blindly" choose a volume. From your article I would now conclude that I would have to install the new BigSur operating system on Macintosh HD because it serves as the "system volume and contains the system files, scripts and the like for macOS". Is that correct?

    • Jen Kleinholz says:

      Hello soho! It is exactly like that. The "Macintosh HD" is the volume with the system and "Macintosh HD Data" is the volume with your data. You shouldn't install a system on it. I am amazed that he even gives you a choice. I would have thought he'd take the "Macintosh HD" right away.

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