Hi @anon76823793,
That is a lot of data. It is possible you may run into some overhead issues with that scale of data. Sync is a much heavier process than traditional backup. I expound on this more in this post, if you would like to take a look: Backup (one-way sync)
As for duplication, If you already have a folder syncing via “sync to odrive”, you do not need to interact with its corresponding content inside the odrive folder. It sounds like you may have performed a recursive sync on C:\users…\odrive\GoogleDrive\Data1 and set folder sync rules to download anything new that arrives in that location. This will sync down the contents there as you push it up from the “sync to odrive” folder. To prevent this duplication, unsync the C:\users…\odrive\GoogleDrive\Data1 folder.