Here's the thing... I have a very slow file copy performance from Windows XP clients to Windows 2008R2 servers. Here are the facts: Windows XP to Windows 2K3: Fast Windows XP to Windows 2K8: Very Slow Windows 7 to Windows (any): Fast

Despite the fact that the obvious solution would be to upgrade to Windows 7, well, we have 900 desktops so it's not an option in the short time.

I have tried everything: Disabling SMB2.0, disabling security signatures, changing the TCP Window size, disabling the W2K8 auto tuning, upgraded the drivers, etc.

We eliminated the network; both the server and the client are connected to the same core switch (no hops, no routers, same VLAN).

Upon monitoring the network with a packet capture utility, we see that the SMB packets being exchanged between the W2K8 and the XP machines are very small packets (256 bytes); despite the fact that the MTUs are properly set (1500) and there is no fragmentation whatsoever. In fact, those SMB packets show, on the IP datagram, that the window is 65535 or close.

The same trace, made using the same application but instead of using a W2K8 share uses a Windows XP share (and that goes FAST) shows SMB packets of 4096 bytes. I can post the traces if necessary.

So, why does XP->W2K8 negotiation arrange for 24-bytes SMB payload, whereas the XP->XP negotiation arranges for 4096 SMB packets?

Any ideas? I am running short of those...