SOFS: Event ID 30818 with SMB Direct for RDMA (KB 3052127)

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One of my customers had an issue after implementing a Scale-Out File Server Cluster:


They are running Windows Server 2012 R2 Systems, which are connected using InfiniBand. The Adapters are using SMB Direct between SOFS Node and Hyper-V Host to establish a Remote Direct Memory Access (RDMA) connection. If you restart a Hyper-V Host you will see Event ID 30818 logged:

Source: SMBClient
Event ID: 30818
Level: Warning
General: RDMA interfaces are available but the client failed to connect to the server over RDMA transport.
Server name: ServerName
Both client and server have RDMA (SMB Direct) adaptors but there was a problem with the connection and the client had to fall back to using TCP/IP SMB (non-RDMA).

You can see, the connection falls back top TCP/IP SMB and you can see this in decreasing Performance…


In Windows Server 2012 R2 the SMB Direct Interface is started automatically by LanmanServer service. If this service starts and tries to open a RDMA connection, before SMB Direct could be loaded, the event is logged. The first connection is established via TCP/IP SMB. All new client connections are established using RDMA.


My customer and the hardware vendor did not stop working on this issue (at this point my praise and respect – all in all it took 4 months), and now the solution could be found…its just a registry key:

Open Registry Editor, and then locate to the following registry subkey:


Right-click the Start registry entry, and then click Modify.
In the Value data box, change the value (by default, it is 3 as on-demand) to 2 (automatic).

This solution is now available for everyone in KB 3052127

So enjoy RDMA…

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