So brother, I have to provide space for initial downloads of around 320 GB.
At the moment I am stopping synchronization, and moving the synchronization process to the primary store.
No, you don't have space for 320 GB. It will download the whole thing, but not store it. That means that once you download 2GB, some files will be deleted, then some more will be downloaded again until you reach 2GB, and so on.