Bandwith from Host to Guest limited by the real ethernet mounted on host.

[Giovanni Toraldo (gionn)]

virtualbox-ose 3.0.6-dfsg-1~bpo50+1 (debian lenny-backports)

I caught a behavior that I wasn't expecting

I have a Debian Lenny amd64 host with a gigabit network card but, unfortunately, attached to a 10/100 switch: 02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)

I setup a Debian Lenny i386 guest with a gigabit network card: 00:11.0 Ethernet controller: Intel Corporation 82545EM Gigabit Ethernet Controller (Copper) (rev 02)

I was hoping that between host and guest, i will get full gigabit speed, but instead, I've host outgoing bandwidth limited by *real* speed.

Here the output of two iperf sessions:

Host -> Guest

[  4] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54853
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.1 sec    114 MBytes  94.1 Mbits/sec
[  5] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54854
[  5]  0.0-10.2 sec    114 MBytes  94.1 Mbits/sec
[  4] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54856
[  4]  0.0-10.2 sec    114 MBytes  94.1 Mbits/sec

Guest -> Host

[  4] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46946
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec    412 MBytes    345 Mbits/sec
[  5] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46947
[  5]  0.0-10.0 sec    402 MBytes    337 Mbits/sec
[  4] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46948
[  4]  0.0-10.0 sec    382 MBytes    320 Mbits/sec

So, it's the outgoing data from host to guest passed to the wire before getting into the guest? Is this an expected behaviour? Should I use a host-only network for having full transfer speeds?

[Frank Mehnert]

What kind of network did you use to check this speed? Bridged? And which ethernet device emulation did you use for the guest? PCNet is probably a bit slower than E1000. Indeed you could try if host-only networking makes a difference.

Apart from this I can assure you that the network speed between guest and host is not limited by VBox nor by the network the host is attached.

[Frank Mehnert]

Should be fixed in VBox 4.0.2.