Catalina: Purpose of /System/Volumes/Data/Previous Content/?

Solution 1:

I think it was originally used for Archive and Install macOS installs. However, you haven't been able to select a Archive and Install for ages.

To me it looks like it is continuously updated in real-time which makes me think its actually linked to the original sources and the files you see are the actual files not copies. It also seems to be well hidden from the file system. Perhaps left there for comparability reasons.

Perhaps look at your drive using DaisyDisk to find where the space is getting used. macOS allows purge-able space take up to 80% of the drive, however, it should automatically reclaim when the storage is required.

https://daisydiskapp.com/manual/4/en/Topics/PurgeableSpace.html?source=PurgeableSpace&appEdition=Standard&appVersion=4.10&osVersion=10.15.5

Solution 2:

For me, I had to first turn off System Integrity Protection which comes with Catalina onwards by rebooting using Command+R and executing this command from the terminal:

$ csrutil disable

Then I rebooted and was able to delete this folder, which in my case was taking up to 700+ GB of disk space:

/System/Volumes/Data/Previous Content

At this point, I was able to delete the above folder which you may need to execute as sudo (see https://discussions.apple.com/thread/250630022):

1. Open Terminal, which is located in the Utilities folder inside the Applications folder.
2. Type rm -rf (don't press Enter / Return just yet)
3. Add a space, then drag the folder into the Terminal window. Hit Enter (Return).

Then after of course I rebooted into the recovery screen using Command+R and re-enabled the system protection with the terminal:

$ csrutil enable

At this point your purgeable content should increase so though you may not immediately see an increase in free disk space the OS will manage this for you if you continue to install more Apps or add files so that you will have the disk space you need until the drive is full.