Hi,
 
I did some tests over my network and got strange results. First, I verified that everything is correctly connected, and that theorical rates are reached (Giga), using two Asus P9X79. The two computers have RAID10 drives : no HDD bottleneck. I used only one of the two Ethernet ports (no support for double connection with the switches).
 
Transfer rates are ok : 110-120MB/s.
 

 
Then I built another machine, using old parts.
 
mobo : Asrock N68-VS3-FX : NForce 630a chipset. I tried different setups, from single IDE HDD to SATA RAID10, with nearly the same results. All useless hardware is disabled, including the onboard Ethernet adapter : replaced with a PCI Giga adapter : SysKonnect SK-9521 v2.0. Jumbo frames enabled everywhere.
 
I got not too bad transfer rates from the Asrock to the P9X79 ; CPU usage 25%, networlk usage : 30%. I think that the PCI bus is the bottleneck : LAN + HDD transfers = bus saturation. Same results with IDE or SATA or SATA RAID.
 
Results with transfer from Asrock to P9X79 :
 

 
Then, from the P9X79 to the Asrock : very bad transfer rate ! I can't explain, and any advice is welcome !
 

The Asrock is intended for downloading, and D/L files have to go to the NAS (a low end model). (28MB/s is normal for this NAS).
 

Then I tested from the Asrock to the NAS, and got an incredible 13.5MB/s !
 

The last test... On the P9X79, I initiated file transfers from the Asrock to the NAS, with Explorer and shared directories. As a result, files go from the Asrock to the P9X79, and from the P9X79 to the NAS. These transfers can easily be seen with the network monitor on the P9X79 : 50% of the NIC bandwidth = 56MB/s (28MB/s+28MB/s, duplex).
 
Now I get nominal transfer rate ! I absolutely don't understand why ! Any advice is more than welcome !
 

 
As you can see, the only way to get nominal write speed on the NAS is to initiate transfers on the workstation. I'd like to understand, and I'd prefer to launch transfers from Remote Desktop, and then let the devices speaking together...
 
Asrock to NAS : only 50%. Asrock -> P9X79 -> NAS : 100%.
 
Weird, is'nt it ?

The switches #2 and #3 are basic switches I got from eBay (but real switches, not hubs)
 
I was amazed by the P9X79 transfer rates : nearly wire speed with 110-120 MB/s, read and write (naturally, with no other traffic on the LAN !). But these X79 mobos are sold as workstation / small server class hardware, and I imagine that two identical machines communicate idealy.
 
About the drivers, the last test illustrated what you wrote !
 
I built another test rig with other old parts. A Asus P7P55D / i5-750. The chipset offers a Giga port I disabled in order to test the same PCI Ethernet card. I let Windows 7 64bit install default Marvel drivers. The P7P55D replaced the Asrock (WinXP 32bit) on the network, with the same disk configuration (software RAID10, but ICH8R). Quick results (I still have to do some more testing) : from P9X79 to P7P55D : 75MB/s, from P7P55D to P9X79 : 57MB/s : good ! (results are reproductible and I do not understand why writes are always faster than reads).
 
Then, I replaced the default drivers with the last ones, downloaded from Marvel website. A disaster ! I restored the default Win7 drivers, and previous performance was back...
 
I will do more testing, now with the onboard adapter. Unfortunately, it is not really usefull as the ICH8R is limited to 2TB volumes. Today, it is not enough to build a backup/archive NAS.
 
How do you get 300-400 MB/s ? Do you use 10Giga hardware, or optical fiber, in a personnal environment ?
 
Needless to say, I know nothing about networks ! All I can do is very basic configuration of a tiny  LAN or Apache personnal server. I do understand nothing to NIC driver parameters and optimisation. And it is probably useless for home or small business networks (?)

Problem fixed !
 
The old Asus P7P55D NIC can transfer larges files at nice rates : 95-110 MB/s through two switches = wire speed. The bottleneck was the disk. I got these results with 4 old 1TB disks in a RAID0 setup. For tests only : RAID0 is not suitable for the backup / file / personnal cloud server I want to build !