Then if you do this how you do you check that the Backups are good or you just the tar archive.
You'd untar them.
That is a full check. But without paying to download the file you just uploaded, you hash the file first and send the hash along with the upload. B2 will hash it when completed and verify that it matches your supplied hash. If it doesn’t, it asks it to reupload.
The Current is part of a VM, NextCloud would be a VM - Why could you not mount both?
How woudl that work? What would NextCloud do with a bunch of random files that have no metadata? They don't exist in the database, what would happen to them?
There's a command you can run that will take a list of files and make them available to a user, I think.
So one user would just get "everything." Or else it's a huge manual process.
Not exactly. Have you ever looked at the file structure of ownCloud/Nextcloud?
Basically in the /data folder there are subfolders per user. You would populate those with the files from the old file server. Then you pop into the CLI and issue this command to rescan the folders and put the stuff in the database.
sudo -u apache php occ files:scan --all -v
You can also do it per user.
I would not recommend ever doing this on an existing system that was not already hosed for some other reason.