From their help page, it looks like everything is CloudStorage, but the data is stored on the external drive in its cache…
Sometimes, users choose a path on another volume to set up OneDrive. A typical use case for this happens when a user has a small internal drive on their Mac, but also has a larger external drive attached.
This configuration is still supported in the new Files On-Demand experience if an external drive is selected during the first-run experience. A few things change as a result:
- The sync root remains in ~/Library/CloudStorage, on the user’s home volume. As noted above, this path cannot be moved from this location.
- The cache path is on the volume that was selected during the first-run experience. This is located in a hidden folder that’s a sibling of the location that was chosen.
- This folder begins with the name “.ODContainer”.
- A symlink is created from the chosen location to ~/Library/CloudStorage.
For example, if the user selects /Volumes/BigDrive/OneDrive for their OneDrive path:
- The sync root will remain in ~/Library/CloudStorage/OneDrive-Personal
- The cache path will be set up at /Volumes/BigDrive/.ODContainer-OneDrive
- A symlink will link from /Volumes/BigDrive/OneDrive to ~/Library/CloudStorage/OneDrive-Personal
Because the cache path is located on an external drive in this scenario, any pinned content will be stored there and not on the main drive.
The cache path folder is hidden by default. Users should not modify this folder or its contents.