Trying to quickly figure out how to copy data between two Synology NAS can include a lot of research and trial and error due to the many ways one can go about doing the task. I found using Shared Folder Sync to be easy and fool proof and provides an exact copy of the data on the receiving NAS.
What is required and how to set Shared Folder Sync up.
Decisions you should make before starting.
How to Set Up Shared Folder Sync
Next Steps - Set Up the Task List
During this part you have options to perform one way sync, two way sync, leave destination file enacted even if the source file were deleted, or delete destination files if source files are deleted.