Very slow network performance with Intel NIC when TCP Large Send Offload is enabled

Question

I have a Windows 2008 server with two NIC's (Intel PRO/1000 PL and Intel PRO/1000 PM), and one virtual external switch connected to each NIC.
With the 01/14/08 network driver, I get very low throughput on both NIC's (~10KB/sec when downloading from my server when it should be around 11MB/sec).
I've found that disabling "TCP Large Send Offload (IPv4)" on the virtual switch and "Large Send Offload v2 (IPv4)" on the physical adapters solves the problem.
Is this a bug in the driver?
Thank you,
Ricardo Costa

Answer 1

2 years later, I was able to get that machine to work with Hyper-V under Windows Server 2008 R2, but only after disabling everything that had anything to do with TCP or IP offloading.  I think that I had to turn off 4 settings on one controller,
and 5 settings on the other controller.  Once that was done, everything worked flawlessly.  It is very apparent that the Virtual Controllers do not properly use many of the features of non-Intel devices (not all Intel devices work either), and
that Hyper-V does not completely uninstall if you remove it.
If you have any problems, start turning off the features that your adapter supports, until it starts working.  You'll need to weight the cost of replacing the controller with a fully supported controller, of which there is no list, or using your existing
controller at a capacity lower than it physically supports.  This has been an elusive issue with Microsoft's Virtual Server projects since they were first in beta, so don't expect a fix anytime soon.
P.S. For those who don't know, the settings are on the actual device and can be changed in the Device Manager.  If you are still having trouble after turning off all the settings, then you will need to replace the controller(s) with a different
make/model.
Bill Bosacker's Blog @ http://www.openSourceC.org/