Different speed connection LINUX - Windows 7

[Mati2580]

Hi
I wonder why there is so much difference in speed connection between LINUX Ubuntu and Windows 7.
I got windows 7 installed on physical machine and ubuntu on virtual machine - two operating systems on one physical machine. Network speed on both systems is 1 Gbit/s, there are two switches on the route to FreeNAS (FreeNAS-8.0.4-RELEASE-p3-x64 (11703)).
I try to copy about 6,5GB of data (via FTP - on the same lan) on two different operating systems and I got something like this:
- Linux ubuntu average speed is 30 MB/s (240 Mbit/s), Windows 7 got almost the same speed - via ftp
But:
- iperf on Ubuntu says my connection is almost 75 MB/s (600 Mbit/s), depends on port I got almost 900 Gbit/s which is pretty nice speed.
- iperf on Windows says my connection is about 25-30 MB/s (200-240 Mbit/s)

Maybe it's the same problem but can you tell me why my connection looks like breathing line? High, low, high, low, ...

Any idea what's going on?

 

[Mati2580]

ok, somethings got change.
When I test by iperf I got speed like this:
- windows 7 -> Freenas = about 240 Mbit/s (30 MB/s)
- windows 7 <- freenas = about 500 Mbit/s (62,5 MB/s)

Cable checked twice,there is only one switch beetwen freenas and windows machine. Both cards on machines are setup on 1Gbit/s.
I missed something in log or debug maybe, but I dont see anything wrong.