Deploying Windows Server 2012 with SMB Direct (SMB over RDMA) and the Chelsio T4 cards using iWARP – Step by Step

1) Introduction

We have covered the basics of SMB Direct and some of the use cases in previous blog posts and TechNet articles. You can find them at

However, I get a lot of questions about specifically which cards work with this new feature and how exactly you set those up. This is one in a series of blog posts that cover specific instructions for RDMA NICs. In this specific post, we’ll cover all the details to deploy the Chelsio T4 series of adapters, the iWARP “flavor” of RDMA.


2) Hardware and Software

To implement and test this technology, you will need:

  • Two or more computers running Windows Server 2012
  • One or more Chelsio T4 cards for each server
  • One or more 10GbE switches
  • Two or more cables as required for the Chelsio T4 cards (typically SFP+ connectors)

Chelsio states support for Windows Server 2012 SMB Direct and Kernel-mode RDMA capabilities on the following adapter models:

  • Chelsio T420-CR adapters (dual-port 10GbE card with iWARP support)
  • Chelsio T440-CR adapters (quad-port 10GbE card with iWARP support)

You can find more information about these adapters on Chelsio’s web site at

Note: The memory-free T4 adapters do not support SMB Direct. That includes the T420-SO-CR.


3) Download and update the drivers

Chelsio is has drivers for Windows Server 2012 with RDMA support. That includes a WHQL certified driver available for public download.

The latest Chelsio T4 driver for Windows Server 2012 can be downloaded from: (look for the Windows Server 2012 driver that is WHQL certified).

The site also offers a README file, Release notes and a User Guide. These are specific for Windows Server 2012, and you should definitely review them before installing the driver.

To update to the new driver, run the executable file and follow the wizard. The software will copy the driver files and install them, prompting for a restart at the end of the process.

This driver should also be available via Windows Update, so you can get it by simply checking for updates on your Windows Server.

4) Configure IP Addresses

After you have the drivers in place, you should configure the IP address for your NIC. If you’re using DHCP, that should happen automatically, so just skip to the next step.

For those doing manual configuration, assign an IP address to your interface using either the GUI or something similar to the PowerShell below. This assumes that the interface is called RDMA1, that you’re assigning the IP address to the interface, that your default gateway is at and that your DNS server is at

Set-NetIPInterface -InterfaceAlias RDMA1 -DHCP Disabled
Remove-NetIPAddress -InterfaceAlias RDMA1 -AddressFamily IPv4 -Confirm:$false
New-NetIPAddress -InterfaceAlias RDMA1 -IPAddress -PrefixLength 24 -Type Unicast -DefaultGateway
Set-DnsClientServerAddress -InterfaceAlias RDMA1 -ServerAddresses

5) Configure the firewall

iWARP uses TCP/IP for communications, so you need to configure the Firewall to allow that traffic. You essentially need to add a firewall rule to the SMB Server to allow incoming traffic from the SMB Direct clients. In Windows Server 2012, SMB Direct with iWARP uses TCP port 5445, in addition to the traditional 445 port used for SMB.

Here’s how you would enable the built-int firewall rule using a PowerShell cmdlet on the SMB server to allow access by the clients:

Enable-NetFirewallRule FPSSMBD-iWARP-In-TCP

Note that the FPSSMBD-iWARP-In-TCP is preconfigured for all Windows Servers and it essentially allows incoming traffic on port 5445. It should only be enabled for systems with iWARP network interfaces with the proper drivers for SMB Direct usage.

If you have multiple SMB servers, you will need to enable this firewall rule on every server that will use SMB Direct with iWARP.

6) Allow cross-subnet access (optional)

One of the main advantages of iWARP RDMA technology is the ability to be routed across different subnets. While the most common setup is a single subnet (or maybe even single rack) deployment, you can use the Chelsio T4 cards to connect computers across subnets. However, this capability is disabled by default on Windows Server  2012 since not everyone will require it.

To enable Network Direct (and therefor SMB Direct) in this fashion, you do need to configure every system (SMB Servers and SMB Clients) to allow routing RDMA across subnets. This is done using the following PowerShell cmdlet:

Set-NetOffloadGlobalSetting -NetworkDirectAcrossIPSubnets Allow
Disable-NetAdapter -InterfaceAlias RDMA1
Enable-NetAdapter -InterfaceAlias RDMA1

Note: Disabling and re-enabling the interface makes the settings change effective without a reboot.

We recommend that you apply the configuration change above before creating any shares. If you do happen to apply it (or make any other major network configuration changes), the SMB client will re-evaluate its connections when new interfaces are detected or every 10 minutes. You can also tell SMB to update its connections immediately by using the following cmdlet on the SMB clients:


7) Verify everything is working

Follow the steps below to confirm everything is working as expected:

7.1) Verify network adapter configuration

Use the following PowerShell cmdlets to verify Network Direct is globally enabled and that you have NICs with the RDMA capability. Run on both the SMB server and the SMB client.

Get-NetOffloadGlobalSetting | Select NetworkDirect

7.2) Verify SMB configuration

Use the following PowerShell cmdlets to make sure SMB Multichannel is enabled, confirm the NICs are being properly recognized by SMB and that their RDMA capability is being properly identified.

On the SMB client, run the following PowerShell cmdlets:

Get-SmbClientConfiguration | Select EnableMultichannel

On the SMB server, run the following PowerShell cmdlets:

Get-SmbServerConfiguration | Select EnableMultichannel
netstat.exe -xan | ? {$_ -match "445"}

Note: The NETSTAT command confirms if the File Server is listening on the RDMA interfaces.

7.3) Verify the SMB connection

On the SMB client, start a long-running file copy to create a lasting session with the SMB Server. While the copy is ongoing, open a PowerShell window and run the following cmdlets to verify the connection is using the right SMB dialect and that SMB Direct is working:

netstat.exe -xan | ? {$_ -match "445"}

Note: If you have no activity while you run the commands above, it’s possible you get an empty list. This is likely because your session has expired and there are no current connections.

8) Review Performance Counters

There are several performance counters that you can use to verify that the RDMA interfaces are being used and that the SMB Direct connections are being established. You can also use the regular SMB Server and and SMB Client performance counters to verify the performance of SMB, including IOPs (data requests per second), Latency (average seconds per request) and Throughput (data bytes per second). Here's a short list of the relevant performance counters.

On the SMB Client, watch for the following performance counters:

  • RDMA Activity - One instance per RDMA interface
  • SMB Direct Connection - One instance per SMB Direct connection
  • SMB Client Shares - One instance per SMB share the client is currently using

On the SMB Server, watch for the following performance counters:

  • RDMA Activity - One instance per RDMA interface
  • SMB Direct Connection - One instance per SMB Direct connection
  • SMB Server Shares - One instance per SMB share the server is currently sharing
  • SMB Server Session - One instance per client SMB session established with the server

9) Review the connection log details (optional)

SMB 3.0 now offers a “Object State Diagnostic” event log that can be used to troubleshoot Multichannel (and therefore RDMA) connections. Keep  in mind that this is a debug log, so it’s very verbose and requires a special procedure for gathering the events. You can follow the steps below:

First, enable the log in Event Viewer:

  • Open Event Viewer
  • On the menu, select “View” then “Show Analytic and Debug Logs”
  • Expand the tree on the left: Applications and Services Log, Microsoft, Windows, SMB Client, ObjectStateDiagnostic
  • On the “Actions” pane on the right, select “Enable Log”
  • Click OK to confirm the action.

After the log is enabled, perform the operation that requires an RDMA connection. For instance, copy a file or run a specific operation.
If  you’re using mapped drives, be sure to map them after you enable the log, or else the connection events won’t be properly captured.

Next, disable the log in Event Viewer:

  • In Event Viewer, make sure you select Applications and Services Log, Microsoft, Windows, SMB Client, ObjectStateDiagnostic
  • On the “Actions” page on the right, “Disable Log”

Finally, review the events on the log in Event Viewer. You can filter the log to include only the SMB events that confirm that you have an SMB Direct connection or only error events.

The “Smb_MultiChannel” keyword will filter for connection, disconnection and error events related to SMB. You can also filter by event numbers 30700 to 30706.

  • Click on the “ObjectStateDiagnostic” item on the tree on the left.
  • On the “Actions” pane on the right, select “Filter Current Log…”
  • Select the appropriate filters

You can also use a PowerShell window and run the following cmdlets to view the events. If there are any RDMA-related connection errors, you can use the following:

Get-WinEvent -LogName Microsoft-Windows-SMBClient/ObjectStateDiagnostic -Oldest |? Message -match "RDMA"

10) Conclusion

I hope this helps you with your testing of the Chelsio T4 cards. I wanted to covered all different angles to make sure you don’t miss any relevant steps. I also wanted to have enough troubleshooting guidance here to get you covered for any known issues. Let us know how was your experience by posting a comment.