Recently, I ran into a frustrating SMB file transfer issue after upgrading my client machine to Windows 11 24H2. After thorough troubleshooting, I found the root cause and a simple fix. I’m sharing this to help others facing similar problems.
Problem
- NAS model: Western Digital MyCloud Mirror Gen2 (firmware 2.13.108)
- Client OS: Windows 11 24H2
- Network setup: Mikrotik RouterOS 7, all devices connected at 1Gbps
- Symptoms:
- Direct connection (laptop ↔ NAS) via a single Ethernet cable → ~60 MB/s (expected speed)
- Through the router → ~8 MB/s over SMB
- iperf tests from both the router and Windows client → ~800 Mbps+ (no issue with the network itself)
- Another identical NAS on the same network → normal speed
Root Cause
After ruling out network and router issues (including FastTrack rules, queues, duplex mismatches, etc.), I discovered:
- Windows 11 24H2 enforces SMB signing (RequireSecuritySignature=1) by default.
- Older NAS devices (like MyCloud Mirror Gen2) support SMB 3.0 but either lack efficient signing implementation or are not optimized for signed sessions.
- This results in significant performance degradation during SMB transfers.
Solution
On the Windows 11 client, disable mandatory SMB signing with these commands (run as Administrator in Command Prompt or PowerShell):
reg add "HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters" /v RequireSecuritySignature /t REG_DWORD /d 0 /f
reg add "HKLM\SYSTEM\CurrentControlSet\Services\LanManServer\Parameters" /v RequireSecuritySignature /t REG_DWORD /d 0 /f
Then, restart the SMB client service:
net stop workstation
net start workstation
Or simply reboot the system.
Result
SMB file transfer speed returned to ~80+ MB/s
No changes were needed on the NAS or router
iperf and SMB performance are now consistent
Caution
Disabling SMB signing reduces SMB session security (it becomes more vulnerable to man-in-the-middle attacks). In a trusted LAN environment, this is generally acceptable. Never disable SMB signing if your SMB server is exposed to untrusted networks or the internet.
