[Samba] Samba fileserver limited to 50 MB/s on gbit

[Leo B.]

Hello,

I am running a fileserver with smbd here.
The server is a 64bit 2.8 GHz Celeron D with 2GB RAM, running 64bit Debian, 
Samba version 3.0.23c.
It is running as a pure fileserver so its only CPU load is serving files.
The client I am doing the tests from is WinXP Pro SP2.
It is connected via Intel e1000 gbit ethernet (both the server and client 
use e1000 chipsets).
I have done a raw tcp benchmark (using netio) and the network IS capable of 
transferring 120 MB/s.

The problem is: The maximal transferrate when reading from the fileserver is

limited to almost exactly 50 MB/s.
The 50 MB/s are reached when the file I'm using for the benchmark is 
completely cached in the fileserver's RAM.
CPU usage while reading:
smbd is using around 10%, top says:
Cpu(s):  2.0%us,  6.0%sy,  0.0%ni, 82.0%id,  0.0%wa,  0.0%hi, 10.0%si,
0.0%st

The only network option my smb.conf contains is:

socket options = TCP_NODELAY IPTOS_LOWDELAY SO_SNDBUF=65536 SO_RCVBUF=65536

- which is everything I could google for optimizing the samba network speed.

I have this problem since I set up the fileserver almost a year ago, my 
debian packages have always been up to date.
I also tested it with a friend's notebook with a new XP installation and did

not get over 50 MB/s so I doubt that my XP is borked.

Can someone please investigate this issue?
I am willing to help testing.

Thanks, Leo B.