Windows Server 2019 File Transfer Speed Issues

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Installing Windows Server 2019 in a Virtual Machine for a customer we experienced severe speed issues with file transfers and in particular issues with large pdf files opened across the network with Acrobat.

Research shows this was likely caused by Receive Segment Coalescing (RSC) a new feature in Server. RSC in short aggregates TCP connections. Windows 7 doesn’t deal well with RSC. The issue was resolved when I disabled RSC. MS Knowledge base articles describe how to do this in a few commands.

This applies to the Virtual Switches created when creating a VM.

Configure RSC in the vSwitch

By default, on external vSwitches, RSC is enabled.

View the current settings:PowerShellCopy

Get-VMSwitch -Name vSwitchName | Select-Object *RSC*

Enable or Disable RSC in the vSwitch

 Important

Important: RSC in the vSwitch can be enabled and disabled on the fly without impact to existing connections.

Disable RSC in the vSwitchPowerShellCopy

Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $false

Re-enable RSC in the vSwitchPowerShellCopy

Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $True

https://docs.microsoft.com/en-us/windows-server/networking/technologies/hpn/rsc-in-the-vswitch

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