On a current client engagement, the Spectrum engineering team was working to migrate around 20TB of Veeam data over to a new physical host with a larger capacity.  The server utilized a mix of 1Gb and 10Gb network connections.  

The team segregated the 10gb nics onto their own network with connections to a Cisco 10gb switch utilizing a dedicated IP subnet for each host to transfer the data.  

We witnessed an issue that even though the team dedicated a 10gb network connection between the host, the data transfer was only occurring at 1gb network speeds.  After some investigation, and a reconfiguration we indeed found that the transfer was occurring over the wrong interface, saturating the 1gb connection.

Could this be the dreaded SMB multichannel issue  that we remember seeing when SMB3 was released in WIndows Server 2012 – Indeed it was!

The resolution that was implemented was to disable multichannel temporarily on both servers

Disable Multichannel on the SMB server side:

Set-SmbServerConfiguration -EnableMultiChannel $false

Disable Multichannel on the SMB client side:

 Set-SmbClientConfiguration -EnableMultiChannel $false

You should only have to disable it on either the client or server side to ensure that it is no longer used.  The systems should be rebooted to ensure the settings take.


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