RSC in the vSwitch
Applies to: Azure Stack HCI, version 20H2; Windows Server 2019
Receive Segment Coalescing (RSC) in the vSwitch is a feature in Windows Server 2019 and Windows 10 October 2018 Update that helps reduce host CPU utilization and increases throughput for virtual workloads by coalescing multiple TCP segments into fewer, but larger segments. Processing fewer, large segments (coalesced) is more efficient than processing numerous, small segments. To learn more, see Host network requirements for Azure Stack HCI.
Windows Server 2012 and later included a hardware-only offload version (implemented in the physical network adapter) of the technology also known as Receive Segment Coalescing. This offloaded version of RSC is still available in later versions of Windows. However, it is incompatible with virtual workloads and was disabled once a physical network adapter is attached to a vSwitch. For more information on the hardware-only version of RSC, see Receive Segment Coalescing (RSC).
Scenarios that benefit from RSC in the vSwitch
Workloads whose datapath traverses a virtual switch benefits from this feature.
Host Virtual NICs including:
Software Defined Networking
Storage Spaces Direct
Hyper-V Guest Virtual NICs
Software Defined Networking GRE Gateways
Workloads that are not compatible with this feature include:
Software Defined Networking IPSEC Gateways
SR-IOV enabled virtual NICs
Configure RSC in the vSwitch
By default, on external vSwitches, RSC is enabled.
View the current settings:
Get-VMSwitch -Name vSwitchName | Select-Object *RSC*
Enable or Disable RSC in the vSwitch
Important: RSC in the vSwitch can be enabled and disabled on the fly without impact to existing connections.
Disable RSC in the vSwitch
Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $false
Re-enable RSC in the vSwitch
Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $True
For more information, see Set-VMSwitch.