Q: How can I restrict SMB multichannel to a specific set of network connections?

A: One of the new Windows Server 2012 features regarding SMB 3.0 is the ability for multiple channels to be used for an SMB session. This means that if multiple paths are available between a client and server, all can be used concurrently to increase the performance and speed of the SMB session.

For example, if an SMB client had three 1Gbps network connections and all could connect to the SMB server, then a total of 3Gbps could be used for SMB transport. There might be times where it's desirable to restrict the network cards used for SMB to a particular SMB server.

This is done by using the New-SmbMultichannelConstraint Windows PowerShell cmdlet, passing the interfaces that should be used. Here's an example:

New-SmbMultichannelConstraint -ServerName <target server> -InterfaceIndex <index of NIC1 to use>,<index of NIC2 to use>

(e.g., New-SmbMultichannelConstraint -ServerName fileserv01 -InterfaceIndex 1,3), and

New-SmbMultichannelConstraint -ServerName <target server> -InterfaceAlias <alias of NIC1 to use>,<alias of NIC3 to use>

(e.g., New-SmbMultichannelConstraint -ServerName fileserv01 -InterfaceAlias 'Mgmt NIC1', 'Mgmt NIC2').

Details of the network cards can be found by using this PowerShell cmdlet:

Get-NetAdapter

which shows the name (alias) and index number of each network card, as in this example:

PS C:\> Get-NetAdapter Name InterfaceDescription ifIndex Status MacAddress ---- -------------------- ------- ------ ---------- LM NIC Intel(R) PRO/1000 PT Dual Port Ser...#2 17 Up 00-15-17-3A... Cluster NIC Intel(R) PRO/1000 PT Dual Port Serve... 16 Up 00-15-17-3A... VM Team 2 NIC Intel(R) Gigabit ET Dual Port Serv...#2 14 Not Present 90-E2-BA-06... VM Team 1 NIC Intel(R) Gigabit ET Dual Port Server... 12 Not Present 90-E2-BA-06... VM NIC Intel(R) 82575EB Gigabit Network C...#2 15 Up 00-15-17-C4... Mgmt NIC Intel(R) 82575EB Gigabit Network Con... 13 Up 00-15-17-C4...

Remember, however, that changing the SMB multichannel configuration isn't something that should be done under normal circumstances, and SMB does a great job of dynamically choosing connections as needed.

TAGS: Windows 8
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