Deleted Macintosh HD, left HD - Data alone - need help connecting the two after restore

Hey all!


My understanding of the whole Macintosh HD and Macintosh HD - Data in Catalina was that you could delete, restore, modify the OS without affecting your data. I was having issues with my Catalina OS, so what I did was format the Macintosh HD drive while leaving the Macintosh HD - Data drive alone. I then installed Catalina onto the Macintosh HD drive.


When it was done, I assumed it would associate itself with the pre-existing Data drive, but it didn't. Instead, it created a new Data drive and during setup it offered the old one as a drive I could import data from, but it wanted to duplicate the data to the new Data drive, and I don't have enough disk space to duplicate all the user data.


I tested moving one of the User folders from the old Data drive to the new one, but that didn't allow me to log into that user.


Is there a way for me to somehow tell macOS that the Data drive it should be looking at and associating with is the old one? I'm not sure how else to do this - all of the data is there on the drive, but the OS isn't seeing it as something I can log into as far as the User folder there.


In Disk Utility, it shows the 3 drives:

Macintosh HD - Mount Point: / - this has a little Finder icon on the disk. Under APFS Volume it says macOS 10.15

Macintosh HD - Data - Mount Point: /System/Volumes/Data - this is the new, empty one. It has a little Home icon on the disk. Under APFS Volume it says macOS 10.15

Macintish HD - Data - Mount Points: /Volumes/Macintosh - Data - this is the old one with all the data, there is no icon on the disk. This has no macOS indicator under APFS volume.

Replies

macOS Catalina introduced the concept of separating critical system files from user data by using two volumes in an APFS container. The former are located in Macintosh HD, with the latter in Macintosh HD - Data. They are not separatable. Deleting either APFS volume basically "breaks" the OS.

I have this same issue. When the hard drive ran out of space and I could not delete anything, I deleted the first volume so I could delete files. Now after reinstall I would like to relink it to the original HD - Data folder and remove the new one it created.