Why is macOS Catalina creating a new data volume on Mac?

At first glance, it appears that the macOS Catalina installer simply copies system files to the main hard drive.

your Mac. However, once you have a good look at everything, you will notice that the data is now divided into two volumes. Why is that? We'll look into this below.

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MacOS file system elements

First you need to understand the essence of the new workAPFS (Apple File System) file system in macOS Catalina. It consists of containers. One container can contain several volumes or one. APFS volumes can have 16 unique roles, including System and Data.

• System Volume: This read-only volume contains all operating system files that cannot be modified.
• Data volume:This volume contains everything else, including your folders like Documents, Music, and Movies.

By sharing this data, Apple hopes to preventOverwrite and change important files and folders on your computer. In other words, Catalina protects its system files by storing them in a read-only volume.

Catalina Installer Renames Primary Volumein Macintosh HD - Data. A new volume with system files is also created. Interestingly, both volumes are displayed in the Finder as a single one, and separately they can only be viewed using the Disk Utility.

Using this utility, you can view and manage volumes, including unmounted volumes.

To make two volumes appear as one, Catalina links them using the new firmlinks feature. It allows several volumes to merge and work as one.

As a result, Catalina does not allow changes to critical system files, which means they are protected from viruses and malware.

Another Catalina novelty is the Moved Items folder, which we also recommend reading.