We have a Dell PE2950 file server running Windows 2008, hosting a DFS namespace of ~1.2 TB. This server has two Broadcom 1Gbps NICs teamed together.

When there is high traffic going to the server across the network (greater than 200 Mbps), any Windows 7 client accessing a DFS share at the time experiences severe performance problems.

For example:

• Computer A has an AutoCAD drawing opened directly from the DFS share. Performance is normal, not causing any issues.
• Computer B begins a file transfer, putting a 11GB file onto a different DFS namespace, on the same server
• Computer A immediately notices lag while using AutoCAD. The cursor momentarily freezes within AutoCAD every 10 seconds or so, and any browsing of the DFS share is extremely slow.
• Computer B completes file transfer, and performance resumes to normal for Computer A.

This is only affecting Windows 7 clients, using a variety of hardware (desktop + laptop). All of our Windows XP clients see no performance impact during the file transfer.

Things I have tried with no change:

• Had Computer A work from an entirely different RAID array from the file transfer destination
• Updated NIC drivers on clients and server
• Enabled TCP offload and receive side scaling on the server NIC (previously disabled when the issue began)
• Antivirus disabled during file transfer

I am currently having a user test applications other than AutoCAD when the file transfer occurs, and will update the question with that result.

Does anyone have any recommendations for resolution or additional troubleshooting steps?