10GbE and TCP Window Size?

[TeeJayHoward]

I've got a pair of X520-SR2s connected directly to each other. One box is running Windows 8, the other Windows 2012 R2. If I do an iperf between the two machines, I get a result of 1Gbit/s. If I run iperf with a 1M window, I get 9.9Gbit/s. If I bridge the two interfaces, I get a result of 250Kbit/s.

Obviously, I want these two machines to talk to each other as fast as possible. The problem is, both machines have 1Gbps interfaces in addition to the 10GbE adapter, and the 2012R2 box has a 40Gbps interface too! I can't seem to find a way to set the TCP window to 1M just for the X520-SR2 adapters. Is there a way to let Windows automatically adjust the window?

 

[HotFix]

If I remember correctly you should not be adjusting the TCP Window Size in Windows Server 2008 or later because it's auto-tuning. If you want to tweak some settings to get better performance check out the following links:
General recommendations:
Performance Tuning Network Adapters
More on receive side scaling (ignore the fact that the post is on SAP):
Network Settings, Network Teaming, Receive Side Scaling (RSS) & Unbalanced CPU Load - Running SAP Applications on Microsoft Platform - Site Home - MSDN Blogs
I have also been told to run the Server Performance Advisor (although I have yet to do so myself):
Microsoft Server Performance Advisor

I hope that helps.

 

[Kristian]

Even though this article is about the newer x540 10 gbase-t cards: setting up my x520s like that improved performance a lot.
Confessions Of A 10 GbE Network Newbie - Part 4: SMB3 - SmallNetBuilder