I'm troubleshooting a strange SMB performance problem. My Windows PC connects to a hard drive attached to a Xiaomi Mi Router 3G running OpenWrt 25.12.5 with Samba4. In Windows File Explorer, both reads and writes usually run at only 1.5–2 MB/s and never go above about 3 MB/s.
The same drive reaches roughly 33 MB/s from my Mac and Android TV, using both SMB and DLNA, so the router, drive, and network appear capable of much higher speeds. The Windows PC is connected by Ethernet and reports a 1000 Mbps link. I tested three different cables, installed the latest Realtek driver for my Gigabyte B650M Aorus Elite motherboard, tried Windows' default driver, disabled power-saving and energy-efficiency options, and checked that Windows is fully updated. Wi-Fi produces the same slow result.
I also enabled the relevant Windows SMB file-sharing support, but that did not change the speed. What Windows-specific setting or issue could be causing this severe SMB bottleneck?
3 Answers
The usual driver and cable checks probably aren’t the cause here, especially since the link negotiates at 1 Gbps and Wi-Fi shows the same behavior. The useful next step would be to compare a large single-file transfer with a tool such as robocopy, rather than relying only on File Explorer. That can help determine whether Explorer itself, antivirus scanning, or SMB negotiation is responsible.
Make sure the Windows SMB client is using SMB2 or SMB3 and that you aren’t accidentally connecting through an unusual name-resolution or compatibility path. Mapping the share directly by its IP address and checking the negotiated SMB dialect can help rule that out. Older SMB1 compatibility support generally should not be enabled unless the server requires it.
Since another operating system gets about 33 MB/s from the same storage, the bottleneck is likely somewhere in the Windows client path: real-time antivirus inspection, a security product, filesystem filtering, or a Windows SMB setting. Temporarily testing with security scanning disabled, then checking Task Manager and Event Viewer during a transfer, may reveal whether the CPU, disk, or a filter driver is limiting the connection.
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