Synology DS716+II NAS File Transfer Slowness from Windows 10

With the Synology DS716+II NAS fully set up for link aggregation (a 2Gbps pipe to the home network), I was expecting great things for my first file transfer.  I used a single album music folder (mp4 files, about a dozen songs) as a test upload, and dragged/dropped it onto the network share, then waited... and waited some more - it was horrendous.  After 5 minutes, I cancelled the copy and began my usual ritual of cursing technology and every IT commercial vendor that came to mind. Per the Windows file transfer window, I was getting just around a 150Kb/s transfer rate.

The Synology Knowledge Base was fairly useless, and basically instructed you to make sure that your device was plugged in and you were not running any software which would consume CPU on your NAS.

I am not a network engineer by trade, but have played around with it enough to know that its just as much black magic and voodoo as it is science.  There are so many variables in play and parts that can go wrong, that its always a time consuming effort to track a problem to ground, and this was no exception.  I spent a number of hours working different combinations of switch settings (with/without link aggregation, MTU sizing, etc, etc), swapping out cables, rebooting devices, and if had a goat in my possession, the poor fella would have been sacrificed as well in attempts to appease the network gods.

Ultimately, the problem was traced to Windows 10.

Your mileage may vary, but for my network and workstation configuration, this configuration completely resolved my issue and pushed my transfer speeds from 100 Kb/s up to the neighborhood of 90 MB/s.

Control Panel | Network and Sharing Center | Change Adapter Settings | Ethernet (or your NIC here), then click Properties:

Then click Configure...:

Then switch to the Advanced tab:

Change Speed & Duplex from "auto negotiation" to "1.0 Gbps Full Duplex".  This instantly fixed my transfer speed issue (not even a reboot required).  The new transfer speeds can be seen below, and are much more in line with what I was expecting from a modern NAS.