NIC can’t detect on MS Hyper-V Virtual Machine

I have built 3 clusters using 3 Dell R805's and a Dell MD3000i SAN connected to one switch and had similar issues to what people are saying here. The fix was to disable "IPv4 Large Send Offload". Since doing this all clusters and 40 VM's have not missed a beat. (4 months now).

"Large Send Offload (LSO) is a feature provided by Broadcom network adapters that prevents an upper level protocol such as TCP from breaking a large data packet into a series of smaller packets with headers appended to them. The protocol stack need only generate a single header for a data packet as large as 64 KB, and the adapter hardware breaks the data buffer into appropriately-sized Ethernet frames with the correctly sequenced header (based on the single header originally provided)."

Below is a link to the full article. http://www.sadikhov.com/forum/index.php?showtopic=132434

Are you copying files from one VM to another VM on the same Hyper-V host?

If you're doing a physical to physical transfer, one disk/LUN is reading at full speed, and one is writing at full speed. If you are doing VM to VM transfers on the same storage, you can expect half the throughput because the same set of disks are doing both the reads and the writes.

If the VMs are using independent storage, are you using dynamic disks or pass-through? Dynamic disks have a lot lower overhead in Hyper-V R2, but it's not zero. I wouldn't expect a 50% drop in throughput though.