Windows slow write performances at 10Gbps speed

[Enquiries]

Hi, great video and article, here is my issue.
I have a PC and Mac connected at 10Gpbs to a qnap NAS, all jumbo frame enable, and using speed test by openspeedTest, I get the 10Gbps speed no issue.
Now, with the mac, I can get about 800MB/sec write and 1101 read which is not too bad, even if it would be nice to have a bit more write performances
With the PC, I only get about 500MB/sec write and 900 read, clearly there is a bottleneck on the Windows 11 PC somewhere, do you have any idea how to optimze it? I did use the recommended cmds in
power shell
netsh int tcp set global autotuninglevel=normal

Set-NetAdapterRss -Name "10GbE Adapter Name" -Enabled $true

netsh int tcp set global rss=enabled
netsh int tcp set global ecncapability=disabled
netsh int tcp set global chimney=enabled

The last one does not work by the way, but it really did not change anything...
Thank you

[ed]

You’re absolutely right to expect more from the write performance on the Windows side, especially over 10GbE. Based on what you’ve described, it sounds like the hardware is up to the task, so the bottleneck is most likely software or driver-related.

Here are a few things worth checking or trying:
1. NIC Driver and Firmware
Double-check that the 10GbE adapter in the Windows machine is running the latest driver and firmware from the manufacturer’s site (not just what Windows Update installed).
2. Jumbo Frame Consistency
Ensure all devices, including switches, are consistently set to the same MTU (typically 9000). In some setups, Windows can silently revert to 1500 if the network path isn’t clean.
3. SMB Multichannel
If your adapter supports multiple queues and RSS is active (which you’ve already enabled), ensure that SMB Multichannel is not disabled via group policy or registry. It can help boost throughput significantly on Windows.
4. Storage Write Target
What drive is the data being written to on the NAS? SSD or HDD RAID? If it’s a slower array, Windows may behave more conservatively with buffering and write caching. Also try disabling Windows Defender real-time protection temporarily to see if there’s an impact.
5. Disable Large Send Offload (LSO)
In Device Manager > Network Adapter > Advanced tab, try disabling “Large Send Offload (IPv4 and IPv6)” and test again. Sometimes this offload causes latency with high-throughput transfers.
6. Test with iperf3 on Windows
Use iperf3 with the NAS or Mac as server, and the PC as client to get raw network performance values independent of SMB/file system overhead. That will help narrow down if the issue is truly network-related or something on the file stack.
7. File Copy Method
Try testing with tools like FastCopy or TeraCopy, as the default Windows Explorer copy is not always representative of actual performance, especially with lots of small files.