Introduction

SMB Multichannel is a feature of the SMB 3.x protocol that improves both performance and availability by allowing multiple network connections to be used simultaneously between an SMB client and server. Originally introduced with Windows Server 2012 as part of SMB 3.0, this feature enables the SMB client to automatically discover and utilise multiple network paths.

In Ceph 9.0, SMB Multichannel support focuses on improving throughput and resiliency by exposing multiple network interfaces to SMB clients, allowing them to establish parallel connections when supported.

Objectives

The key objectives of the SMB Multichannel feature are:

• Increase aggregate network throughput by using multiple network interfaces in parallel.

• Improve fault tolerance by allowing SMB sessions to continue even if one network path fails.

• Automatically detect and configure multiple network paths without manual intervention.

• Leverage modern NIC capabilities such as RSS to scale SMB performance efficiently.

Benefits

• Increased Throughput: Data is transmitted concurrently across multiple network adapters, improving overall bandwidth.

• Network Fault Tolerance: SMB clients can continue operating uninterrupted even if one network connection goes down.

• Automatic Configuration: SMB Multichannel automatically discovers available interfaces and negotiates usable channels.

Requirements

To use SMB Multichannel, the following requirements must be met:

• SMB clients and servers running SMB 3.x–capable operating systems (e.g., Windows Server 2012+, Windows 8+).

• Multiple network adapters on the SMB server and/or client.

• One or more network adapters that support RSS (Receive Side Scaling).

• Optional NIC Teaming configuration.

• RDMA-capable adapters (currently not supported in Ceph SMB).

Installation and Configuration

SMB Multichannel is enabled by default on both SMB clients and servers.

• No explicit configuration is required to enable Multichannel.

• The SMB client automatically detects and establishes multiple connections based on available network interfaces.

Disabling SMB Multichannel

In some testing or troubleshooting scenarios, Multichannel may be disabled explicitly.

On the SMB server side:

Set-SmbServerConfiguration -EnableMultiChannel $false

On the SMB client side:

Set-SmbClientConfiguration -EnableMultiChannel $false

How SMB Multichannel Works

1. The SMB client negotiates the SMB 3.x protocol and Multichannel capability with the SMB server.

2. The client requests a list of available server interfaces.

3. The SMB server responds with interface details (such as RSS capability and network speed) using an SMB FSCTL operation.

4. Based on workload characteristics and NIC properties, the SMB client decides whether to establish multiple channels.

Channel selection depends on:

• Client workload

• Number of available NICs

• NIC speed and capabilities (e.g., RSS)

Supported and Unsupported Features

Supported

• Pass-through RSS NIC properties

• Multiple physical NICs

Not Supported (Ceph 9.0)

• NIC Teaming

• RDMA (Remote Direct Memory Access)

Conclusion

SMB Multichannel in Ceph 9.0 brings significant performance and resiliency improvements by allowing SMB clients to leverage multiple network interfaces automatically. While advanced features such as RDMA and NIC Teaming are not yet supported, Multichannel with RSS-enabled NICs already provides meaningful throughput gains and fault tolerance.

This feature is especially valuable in high-bandwidth and highly available file-serving environments, making Ceph SMB a stronger choice for enterprise workloads.