I'm running an Ubuntu 12.04 server x64 guest on Win7 x64 host with VirtualBox and I'm getting pretty terrible network speeds regardless of network mode or adapter.
The best that I've got so far was around 100Mbps guest->host and 20Mbps host->guest (measured with iperf) using bridged mode with virtio adapter. CPU usage during these tests is pretty high but not 100%. The host reports the VBox adapter speed to be 100Mbps and the physical LAN controller is 1Gbps.
Is this due to my hardware (E-450 - http://www.asus.com/Motherboards/AMD_CPU_on_Board/E45M1I_DELUXE/) or can something be done to improve the speed?
I also tried VMWare Workstation but it didn't perform any better and it didn't support raw disk access for my 3TB drives.
This is a home server/HTPC that was originally running just Ubuntu but it didn't perform that well on the HTPC aspect. Linux is vital since I run greyhole to duplicate the important data and pool the drives. I'd very much like to take full advantage of the system with both Windows and Ubuntu but if nothing can be worked out, I guess I'll return to just Ubuntu and try to make the most of it.