I have the following setup (excuse "ASCII Art"):
laptop SSD (attached via SATA) <-> 1Gbps wired ethernet <-> server HDD (attached via USB3.0)
Where laptop and server both run Windows Server 2012 R2, and the server drive is mounted on the laptop via standard Windows "Advanced File Sharing" (i.e., standard Windows 8 era SMB).
Now, I do file transfers via the command line (robocopy).
Server to laptop: Continuous 330Mbps achieved.
Laptop to server: Continuous 940Mbps achieved.
Why the ~3x speed difference based on direction?