Fix Slow Hyper-V Guest Network on Dell PowerEdge Servers

Introduction:

If you’re experiencing slow network performance with your Hyper-V guest VMs on Dell PowerEdge servers, you’re not alone. In this post, I’ll share my experience with a common issue and the steps I took to resolve it.

Environment:

I’m using Dell PowerEdge R520 servers with Broadcom NetXtreme 1Gb NICs, all running Server 2008R2 SP2. My firmware and drivers are up to date. Notably, this issue has only occurred on the guest VMs; the host and other bare-metal systems are performing well.

Understanding the Issue:

The root of the problem lies in Virtual Machine Queues (VMQ). VMQ enhances throughput for VMs by offloading network processing to the physical adapter. Initially, I disabled VMQ to alleviate the slow network issue, but I wanted to enable it for better performance.

Resolution:

Broadcom NICs have VMQ enabled by default, but for it to function correctly, you need to add a specific registry value. Without this value, slow network performance persists. Here are the steps.

1. Disable VMQ Temporarily: First, disable VMQ in the configuration properties of all physical adapters assigned to your guests under the advanced tab. If you’re using Intel NICs, you can skip this step, as VMQ is disabled by default.
2. Edit the Registry:
   • Open Regedit on your Hyper-V host and navigate to the following location.

HKLM\SYSTEM\CurrentControlSet\Services\VMSMP\Parameters

3. Add the Registry Value:
   • Create a new DWORD value named BelowTenGigVmqEnabled for 1Gb adapters. If you’re using a 10Gb adapter, name it TenGigVmqEnabled.
   • Set the value to 1.
4. Re-enable VMQ: Go back to the physical adapters and enable Virtual Machine Queues.
5. Restart the Physical Server: Restart your Hyper-V host to apply the changes.
6. Start Guest VMs: After the host restart, start your guest VMs so they recognize the updated settings.

Verify:

After starting your guest VMs, check the ping response to verify network performance. Ping your guest VM and compare the response times before and after making the changes. You should see improved performance with consistent ping times under 1ms.

Conclusion:

After following these steps, your network performance issues should be resolved, with pings consistently under 1ms. This adjustment improves network speeds and enhances overall VM performance, eliminating sluggishness in your Dell PowerEdge Hyper-V environment.