server 2022 hyper-v slow network throughput

Question

I stood up a new server 2022 os on a server 2022 host. The system is running on a Dell poweredge server. I did some testing and am only getting 85mbps download speed and getting 300+ mbps on upload. the server is running a 4 port Nic and is completely up to date on drivers and OS patches.

I put together a server 2019 guest box on the same server 2022 host and was rewarded with 554Mbps down and 448Mbps upload speed.

I then tried the same server 2022 guest on the 2019 server host the download speed was 83 Mbps and the upload is 170Mbpsi then went on to our 2019 host and ran the same speed test i got 568 Mbps down and 414 uploadThis should prove that the hardware is sound and the bottle neck is in the server 2022 OSDoes anyone have any more ideas as what to try? thanks

Answer 1

Hello,

There is a Receive Segment Coalescing (RSC) feature in Hyper-V on Windows Server 2019/2022. RSC allows reducing CPU load and improving network throughput by combining multiple TCP segments into larger segments. Network performance is improved because large segments are processed faster than many smaller segments. But if RSC support is enabled, it may cause additional network latency in some hardware configurations.

You can check if RSC is enabled for a virtual switch using the following powershell command:

Get-VMSwitch | Select-Object *RSC*

To disable software RSC for a specific virtual switch, run the following command:

Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $false

Check if the network speed in the Hyper-V VM is improved after disabling RSC. If the network speed is improved, you can disable RSC on the virtual switch to which the VM is connected.

Hope the above information is helpful to you.

Best Regards

Zunhui

Answer 2

RSC is disabled already

Answer 3

Hi chris Rolke,

Thanks for your reply. By default, RSC is enabled on all external switches on Windows Server 2019. I suggest you try to enable RSC on the virtual network switch on Windows Server 2022 to see if it can improve network bandwidth. In addition, if VMQ is enabled in the network adapter driver of the Hyper-V host, it may also cause poor network performance in the Hyper-V virtual machine. It is recommended that you check whether VMQ is enabled on Windows Server 2022, right-click the network adapter on the host, and then check whether VMQ is disabled in "Properties" -> "Configuration" -> "Advanced Options".

Best Regards

Zunhui

Answer 4

I have tried with RSC on and off on the host machine without any improvement

I do not have any option for Virtual Machine Queues

Answer 5

I just wanted to say thank you for this post. I disabled the RSC and my network problems for VM's have been solved. I am running Hyper-V 2019 Cluster with 3 Host and about 80 VM with all different OS levels but it was the 2022 servers that were having the most performance issues. I thought it was SentinelOne or maybe FsLogix that we were deploying. I spent countless hours trying to troubleshoot something that was not there. This online powershell command fixed a couple of weeks of late night digging.