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Caspar-3353 asked CandyLuo-MSFT commented

Slow SMB connection between server 2008R2 and server 2019

We have one server running an old piece of software that only supports server 2008R2 for now.. All of the other servers have been migrated to server 2019.

When we login to the 2008R2 server we have something strange happening. The following actions are done on the actual 2008R2 server.

If we copy files FROM a server 2019 share towards the 2008R2 server the transfer speed is about 8 MB/s. (megabyte) and fluctuates a lot. It takes forever.
If we copy the same files FROM the 2008R2 server towards the server 2019 share the transfer speed is a steady 110 MB/s (megabyte)

Server 2019 is hosted on a Hyper-V 2019 host. 2008R2 is a physical installation on a HP server. Network is gigabit everywhere.

I expect this has something to do with SMB settings on 2019, what would be the first to check? I'm setting up a test VM with server 2019 on that same Hyper-V host.
Just to be clear, the transfer speeds between 2019 servers and the client PC's (Windows 10) is all good.

windows-server
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Caspar-3353 answered CandyLuo-MSFT commented

I have found the solution to this problem. It seems that Server 2019 uses a technique called "receive segment coalescing (RSC)". Server 2008R2 and Windows 7 seem to have trouble with transfer speeds if this function is enabled on Server 2019. I used the following command on the 2019 server using Windows Powershell:

You can check if this function is enabled on your Server 2019 server:

Get-NetAdapterRsc * | FL

after that verify it has been enabled you can run the following command:

Disable-NetAdapterRsc *

This disables the RSC function on the LAN adapter of the 2019 server. After this the 2008R2 server now has a much faster connection sending and receiving data to and from 2019 server. Maybe this isn't the best solution but it works great. The transfer speed in my case went from 8 MB/s to 109 MB/s

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Good to hear that you have solved this issue by yourself. In addition, thanks for sharing your solution in the forum as it would be helpful to anyone who encounters similar issues.
If there is anything else we can do for you, please feel free to post in the forum.

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CandyLuo-MSFT answered

Hi ,

Enabling SMBv1 on server 2019 and see if the performance issue is addressed. For your reference:

How to detect, enable and disable SMBv1, SMBv2, and SMBv3 in Windows

Best Regards,
Candy


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