SMB3 Multichannel Setup Guide: 5 Gbps Over Dual 2.5GbE NAS Ports
To double single-client NAS file transfers from 280 MB/s to 550+ MB/s (5 Gbps) over dual 2.5GbE ports, enable SMB3 Multichannel in Synology DSM 7.2+ (Control Panel > File Services > SMB > Advanced Settings > Others) or TrueNAS SCALE (Shares > Windows SMB Shares). Crucially, you must disable IEEE 802.3ad LACP link aggregation and leave each NAS and PC port on independent IPs.
- Single-Client Speed Doubling: Unlike 802.3ad LACP (which caps one PC to a single physical link), SMB3 Multichannel stripes one file copy across multiple NICs simultaneously for
550+ MB/sover dual 2.5GbE. - Mandatory No-Bonding Rule: Remove any
802.3ador Adaptive Load Balancing bonds on your NAS and switch; assign each port its own IP in the same subnet (e.g.,192.168.1.50and192.168.1.51). - Match Link Speeds & RSS: Both ports on the client and NAS must negotiate identical link speeds (e.g., two
2.5 Gbpsports) and support Receive Side Scaling (RSS). - PowerShell Verification: Run
Get-SmbMultichannelConnectionandGet-SmbClientNetworkInterfacein Windows 11 PowerShell during an active file transfer to confirmRSS Capable = True.
How SMB3 Multichannel Beats 802.3ad LACP for Single-Workstation Speed
For years, home lab builders plugged two Ethernet cables into a dual-port NAS, enabled IEEE 802.3ad Link Aggregation (LACP) on their managed switch, and wondered why copying a 100 GB video file from one desktop PC never exceeded 113 MB/s (1GbE) or 283 MB/s (2.5GbE). LACP distributes traffic using a Layer 2/3 MAC-and-IP XOR hash algorithm that pins any single TCP session to a single physical wire to prevent out-of-order packet arrival.
SMB3 Multichannel—built into the Server Message Block 3.0+ protocol in Windows 10/11, Windows Server, macOS Big Sur 11.3+, and Samba 4.15+—solves this at Layer 7. When a client initiates an SMB session to your NAS over TCP port 445, the server reports all active network interfaces and link speeds via the FSCTL_QUERY_NETWORK_INTERFACE_info IOCTL. The client then opens multiple parallel TCP connections across every matching NIC pair, aggregating two 2.5GbE connections into a true 5 Gbps (550–575 MB/s) pipe on a regular unmanaged switch.
Hardware & Network Requirements (NIC Symmetry, RSS, and IP Addressing)
SMB3 Multichannel enforces strict path selection rules. If one interface negotiates at 2.5 Gbps and the second drops to 1 Gbps due to a bad Cat5e patch cord, the SMB client will exclusively use the faster 2.5GbE adapter and ignore the slower link completely.
- Dual Identical-Speed NICs on Both Ends: Connect two 2.5GbE ports on your NAS (or add a dual-port Intel
I226-V/ RealtekRTL8125BGPCIe card or USB-C 2.5GbE adapter to your PC) into any 2.5GbE switch. - Disable Switch & NAS Link Aggregation: Delete any existing Bond/LAG interfaces in your NAS OS and switch GUI. Each Ethernet port must operate as a standalone interface with its own IPv4 address (such as NAS LAN 1 at
192.168.1.50/24and NAS LAN 2 at192.168.1.51/24). - Single Subnet or Dual Subnets: Connecting all four cables into the same flat
192.168.1.0/24unmanaged switch works out of the box, provided your NIC drivers reportRSS Capable = True. If a USB Ethernet adapter lacks RSS, assign the second NIC pair to a separate subnet (e.g.,192.168.2.0/24).
Enabling SMB3 Multichannel on Synology DSM 7.2+, TrueNAS SCALE & QNAP
Most consumer and prosumer NAS platforms ship with SMB3 Multichannel disabled by default or hidden under advanced file service menus. Follow the exact path for your storage appliance:
- Synology DSM 7.2+: Navigate to Control Panel > Network > Network Interface and confirm any Bond is deleted so
LAN 1andLAN 2hold separate IPs. Next, go to Control Panel > File Services > SMB > Advanced Settings > Others, check Enable SMB3 Multichannel, and click Save. - TrueNAS SCALE (Dragonfish / Electric Eel): Navigate to Shares > Windows (SMB) Shares, click the global Configure Service icon (or go to System Settings > Services > SMB > Edit), click Advanced Settings, check Enable SMB Multichannel, and restart the SMB service.
- QNAP QTS / QuTS hero 5.1+: Open Network & Virtual Switch to verify independent adapter IPs, then navigate to Control Panel > Network & File Services > Win/Mac/NFS/WebDAV > Microsoft Networking > Advanced Options and enable SMB Multichannel.
Verifying RSS & Active Multichannel Sessions in Windows 11 and macOS
Windows 11 Home and Pro enable SMB Multichannel automatically, but driver misconfigurations can silently disable Receive Side Scaling. Open an elevated PowerShell window on your workstation and run these diagnostic commands while copying a large 20 GB file to or from your NAS:
- Check Client NIC RSS Support: Run
Get-SmbClientNetworkInterface. Verify that both of your Ethernet adapters appear with matchingLink Speed(e.g.,2.5 Gbps) andRSS Capable : True. If RSS is disabled, open Device Manager > Network adapters > Properties > Advanced and set Receive Side Scaling toEnabled(with Maximum Number of RSS Queues set to4). - Inspect Active Multichannel Streams: Run
Get-SmbMultichannelConnection. Look forSelected : Trueacross both client-to-server IP pairs and confirmMaxChannelsis2or higher. - Verify on macOS: Start a Finder file transfer and run
smbutil multichannel -ain Terminal to inspect active session bindings and NIC interface indices.
SMB3 Multichannel Performance & Storage Bottleneck Benchmarks
| Link Configuration | Aggregate PHY Bandwidth | Real-World SMB3 Throughput | Minimum NAS Storage Array Required |
|---|---|---|---|
| 2x 1GbE (Dual Gigabit) | 2.0 Gbps | 225–235 MB/s | 2-Bay 7200 RPM HDD RAID 1/0 or SATA SSD cache |
| 2x 2.5GbE (Dual 2.5G) | 5.0 Gbps | 550–575 MB/s | 4-Bay HDD RAID 5/10 + NVMe Read/Write Cache, or All-Flash SATA/NVMe |
| 4x 2.5GbE (Quad 2.5G) | 10.0 Gbps | 1,080–1,140 MB/s | 6+ Bay HDD RAID 10/Z2 with high RAM ARC, or NVMe M.2 SSD Pool |
| 2x 10GbE (Dual 10G) | 20.0 Gbps | 2,150–2,300 MB/s | PCIe Gen4 NVMe U.2/M.2 RAID Array (CPU & PCIe lane limited) |
| Mixed 1x 2.5GbE + 1x 1GbE | 2.5 Gbps (No aggregation) | 280–285 MB/s | SMB3 ignores the 1GbE link; only aggregates equal-speed adapters |
SMB3 Multichannel Setup & Troubleshooting Checklist
- Delete any existing 802.3ad LACP or Balance-ALB bond on your NAS and managed switch so every NIC port gets its own IP address.
- Verify all Ethernet ports on the workstation and NAS negotiate at the exact same speed (e.g., 2500 Mbps Full Duplex).
- Enable SMB3 Multichannel in Synology DSM (Control Panel > File Services > SMB > Advanced > Others) or TrueNAS SCALE SMB service settings.
- Run Get-SmbClientNetworkInterface in Windows PowerShell to confirm RSS Capable is True on both local network adapters.
- Mount your NAS shared folder using its primary IP address or hostname and start a 10+ GB sequential file copy.
- Run Get-SmbMultichannelConnection in PowerShell or inspect Windows Task Manager > Performance > Ethernet to see traffic split 50/50 across both NICs.
Frequently Asked Questions
Can I use SMB3 Multichannel on an unmanaged 2.5GbE switch?
Yes. Because SMB3 Multichannel operates at Layer 7 using standard independent IP addresses and TCP port 445 sessions, it works on any inexpensive unmanaged 5-port or 8-port 2.5GbE switch without requiring managed VLAN or LACP support.
Does SMB3 Multichannel work with only one Ethernet cable on my PC and two on my NAS?
Only if your PC's single Ethernet port is faster than the NAS ports—for example, a PC with one 5GbE or 10GbE NIC connected to a switch where the NAS has two 2.5GbE ports—and the PC's NIC supports Receive Side Scaling (RSS). If both the PC and NAS only have 2.5GbE ports, you need two cables on the PC and two on the NAS to reach 5 Gbps.
Why does my dual 2.5GbE SMB Multichannel transfer start at 560 MB/s and drop to 190 MB/s halfway through?
Your network configuration is working properly, but you have exhausted your NAS RAM cache (ARC) or NVMe write cache and hit the sustained mechanical write speed limit of your spinning SATA hard drives. Adding an NVMe SSD read/write cache or reading from an SSD storage pool will sustain 560 MB/s continuously.
Should I assign my second NAS and PC Ethernet ports to a separate subnet like 192.168.2.x?
Using a single subnet (all ports on 192.168.1.0/24 via DHCP reservations) is easiest and works reliably as long as your NICs report RSS Capable = True. However, assigning the second NIC pair to a dedicated unrouted subnet (such as 192.168.2.10 and 192.168.2.50 with no default gateway) is a proven workaround when using USB 2.5GbE adapters whose drivers lack RSS.
Related Wired LAN Setup & Engineering Guides
- 802.3ad LACP Link Aggregation Setup Guide for Switches & NAS — Learn how to configure IEEE 802.3ad LACP link aggregation on UniFi, TP-Link Omada, and Netgear switches, plus why LACP vs SMB3 Multichannel differs for a NAS.
- How to Set Up a Network Switch — Set up an unmanaged or smart managed Ethernet switch: connect the router LAN uplink, read link speed LEDs, prevent switching loops with RSTP, and set VLANs.
- Cat5e vs Cat6 vs Cat6a Ethernet Cables Compared — Compare Cat5e, Cat6, and Cat6a Ethernet cables across 1Gbps, 2.5GbE, and 10GBASE-T distances, MHz bandwidth, PoE heat, CMR vs CMP, and solid copper vs CCA.
- Small Business Network Setup Checklist — Build a reliable small business network with our checklist covering Dual-WAN failover, 4-VLAN segmentation, PoE budgets, UPS sizing, and WPA3 WiFi security.