Hyper V upgrade from 2019 to 2025 shows throughput issues

Question

Windows server is upgraded to 2025 and new instance for hyperV is up and running.

I have tried enabling SRIoV, But still I am observing lower throughput than what we have achieved earlier. We see ~50% of degradation in throughput from 2019 to 2025 upgrade. We need support to fix the issue.

Answer 1

Hello Ramapriya Rajamani (ramrajam),

The 50% throughput degradation you are seeing after moving from Windows Server 2019 to 2025 with Hyper‑V, even with SR‑IOV enabled, is not a generic configuration issue but points to changes in the network stack and driver interaction with the new kernel. SR‑IOV itself only bypasses the virtual switch datapath; if throughput is still halved, the bottleneck is either in the NIC firmware/driver compatibility with the 2025 kernel, or in the way the vSwitch and VMQ/VMMQ queues are being handled post‑upgrade.

The first thing to validate is that the NIC drivers are the latest vendor‑certified versions for Windows Server 2025. Inbox drivers provided by Microsoft often lag behind vendor releases, and with SR‑IOV the NIC firmware and driver must match the OS kernel capabilities. For Intel adapters, confirm you are running the latest PROSet package; for Mellanox or Broadcom, check the vendor’s support matrix for Server 2025. Outdated drivers are the most common cause of degraded throughput after major OS upgrades.

Next, check whether VMQ and VMMQ are enabled and properly balanced. In Server 2019, VMQ scaling was stable, but in Server 2025 the default queue allocation logic changed. Run Get-NetAdapterVmq and Get-NetAdapterSriov on the host to confirm queues are active and mapped correctly. If you see queues pinned to a small subset of cores, you may need to adjust RSS/VMQ processor affinity using Set-NetAdapterVmq to spread load across NUMA nodes.

Also confirm that the virtual switch is configured with the correct offload settings. In Server 2025, some offloads (such as RSC and RDMA) are disabled by default in certain configurations. Run Get-NetAdapterAdvancedProperty and check that Large Send Offload (LSO), Receive Side Scaling (RSS), and SR‑IOV are all enabled.

If you are still seeing degradation after driver and queue validation, disable VBS (Virtualization Based Security) temporarily on the host. The 2025 kernel enforces additional isolation that can impact NIC performance in SR‑IOV scenarios. This is documented in Microsoft’s performance tuning guidelines for Hyper‑V.

Finally, check whether the throughput drop is consistent across all NICs and VMs or isolated to specific adapters. If it is consistent, this is likely a regression in the 2025 networking stack. In that case, you should open a support case with Microsoft and reference the performance delta between 2019 and 2025 with SR‑IOV enabled. Microsoft has historically released hotfixes for similar regressions in Hyper‑V networking after major version upgrades.

In short, update NIC drivers and firmware to 2025‑certified versions, validate VMQ/VMMQ queue distribution, confirm offload settings, and test with VBS disabled. If degradation persists, escalate to Microsoft Support as this is likely a kernel‑level regression.

I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!

Domic Vo.

Answer 2

Hello, we have hypervisors running on Windows 2025 Datacenter.

We've encountered a lot of network issues.

I’ve tried many different configurations, and here’s what I’ve found:

Dell R760 with 2 Intel 810 cards and Broadcom 25/28 Gb cards

Hyper-V 2025 works very well if the VMs are running Windows 2025

Advanced networking features are not supported by Linux VMs or versions of Windows prior to 2025

I had to disable VMQ on the Broadcom cards

SRIOV is enabled on both Intel and Broadcom cards

For Broadcom cards: receive buffer = 5000 and transmit buffer = 3000

For Intel cards: receive buffer = 4096 and transmit buffer = 2048

For VMs in 2025, you can check SRIOV in the network settings and disable VMQ

For other systems, uncheck SRIOV and leave VMQ checked (even if it’s not active on Broadcom cards)

Jumbo frames: not necessarily useful on the client-side workstation network because users’ computers have an MTU of 1500 (or 1514), and this causes fragmentation

Memory priority management doesn’t really work; it has caused some servers to crash

On hypervisors and VMs 2025, you have to change the congestion protocol, especially Compat = CTCP

netsh int tcp set supplemental template=internet congestionprovider=CUBIC

netsh int tcp set supplemental template=internetcustom congestionprovider=CUBIC

netsh int tcp set supplemental template=Datacenter congestionprovider=CUBIC

netsh int tcp set supplemental template=Datacentercustom congestionprovider=CUBIC

netsh int tcp set supplemental template=Compat congestionprovider=CTCP

Answer 3

Bonjour, nous avons des hyperviseurs sous windows 2025 datacenter.

nous avons recontré beacoup de difficultés avec le réseau.

j'ai essayé beaucoup de combinaisons et voici ce qui en ressort :

Dell R760 avec 2 intel 810 et cartes broadcom 25/28 gb

• Hyper-V 2025 fonctionne très bien si les VM sont en windows 2025
• les fonctionnalités avancées du réseau ne sont pas comprises par les VM linux et les versions de windows antérieures à 2025
• j'ai du désactiver le VMQ sur les cartes broadcom
• SRIOV est actif sur les cartes Intel et broadcom
• pour les broadcom, receive buffer = 5000 et transmit buffer = 3000
• pour les Intel, receive buffer = 4096 et transmit buffer = 2048
• pour les VM en 2025, on peut cocher VMQ et SRIOV dans les fonctions réseau
• pour le reste, décocher SRIOV et laisser VMQ (même s'il n'est pas actif sur les broadcom)
• sur les Hyperviseurs, pour le congestion control laisser CUBIC
• jumbo frame : pas forcément utile sur le réseau coté client workstation car les ordinateurs des utilisateurs sont en mtu 1500 (ou 1514) et cela apporte de la fragmention
• la gestion de la priorité mémoire ne fonctionne pas vraiment, cela a fait planter quelques serveurs

d'autres commandes utiles :

netsh interface tcp set global initialRto=2000

netsh interface tcp set global autotuninglevel=normal

Set-SmbServerConfiguration -EnableMultiChannel $true

Set-VMSwitchTeam -Name "vSwitch-name" -LoadBalancingAlgorithm Dynamic

voici ci-dessous 2 exemples : 3cx (VMQ) + file server sous windows 2025 (SRIOV)

windows 2022 ou 2016 = VMQ

toutes les VM windows server ont une taille fixe pour le fichier d'échange

pour le File server SMB, utiliser les optimisations suggérées par Microsoft

processeur RSS = 6 qui vont de 2 à 7

Cela fonctionne chez moi mais cela ne garantit pas que cela fonctionnera chez vous

Answer 4

What are the settings needed to ensure that network configuration and switches are set up for optimal performance?

"Check Network Configuration: Verify the network configuration settings for the virtual switches and ensure that they are correctly set up for optimal performance."

Answer 5

If you are experiencing throughput issues after upgrading from Windows Server 2019 to 2025 with Hyper-V, consider the following troubleshooting steps:

1. Update Drivers and Firmware: Ensure that all network adapter drivers and firmware are up to date on both the Hyper-V host and the virtual machines.
2. Check Network Configuration: Verify the network configuration settings for the virtual switches and ensure that they are correctly set up for optimal performance.
3. Review Resource Allocation: Check the resource allocation for your VMs. Ensure that they have adequate CPU and memory resources assigned to them, as insufficient resources can lead to performance degradation.
4. Enable SR-IOV: Since you mentioned enabling SR-IOV, ensure that it is properly configured. Sometimes, additional settings may need to be adjusted in the network adapter properties.
5. Monitor Performance: Use performance monitoring tools to identify any bottlenecks in the network or storage subsystems that may be affecting throughput.
6. Check for Known Issues: Look for any known issues related to Hyper-V on Windows Server 2025 that might be causing the degradation. Sometimes, specific updates or patches may be necessary to resolve performance issues.

If these steps do not resolve the issue, consider reaching out to Microsoft Support for further assistance.

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References:

• Troubleshoot Hyper-V virtual machine performance
• Hyper-V GPU assignment, partitioning, and passthrough troubleshooting guidance
• Resolved issues in Windows Server 2025
• Multipath I/O (MPIO) troubleshooting guidance