Strange LAN Transfer Speed (Async Write & Read)


Sep 30, 2010
I have a strange problem with transferring files between 2 computers connected to each other through an ethernet cable. Both PCs have on-board gigabit ethernet ports. Aside from the different hardwares, the softwares (especially network settings) are configured almost the same, with Windows 7 x64 etc. Tests have been taken with and without antivirus programs running with no difference. Duplex settings are auto negotiation. Jumbo packets (~9MB) are enabled (usually I'm transferring really large files). Hard drives are not a problem, since local transfer speed within a computer is around 100 MB/s.

Now if I am on PC1, and accessing shared files on PC2: Transferring files from PC1 to PC2 is very fast, usually in the range of 60 MB/s (see results below from LAN SpeedTest). But the opposite (transferring from PC2 to PC1) is really slow, about 10 MB/s.

If I am on PC2, and accessing PC1: Transferring files from PC2 to PC1 is slow (see speed test below - it's actually a little slower than when I'm transferring files and reading the speed report from Windows), while the opposite is fast (also about 60 MB/s like in the first case)

So what causes this?



google tcp window scaling and disable it. worked for me. ( netsh int tcp set global autotuninglevel=disabled )

Win7 x64. went from 15MBytes/sec to 114MBytes/sec

The default values work fine for normal networks. The main feature is that it can scale itself larger for higher latency connections, but this is mostly good for sat links, so it doesn't help much on regular cable/dsl/Lan.


Dec 28, 2011
Thank you!
i was having a similar problem and this solved it. I thought the problem was with my WD My Book World Edition, suddenly having a very slow transfer (write) speed, but then noticed that its the case even when I access other network computers.
I still wonder why it changed in the first place...