[Samba] Samba Variables and TCP/IP Throughput

[AndyLiebman at aol.com]

Hi, 

I am trying to optimize my gigabit network. I have two Intel 1000 MT Gigabit 
Server Adapters, which support Jumbo Frames -- as well as a Switch that 
supports Jumbo Frames. However, I am observing some strange behavior in my file 
transfers from Windows XP to Linux and I am wondering if it has anything to do 
with the way the Samba variables are set on my Linux box? 

The "strange behavior" is that when I set both NICs to use Jumbo Frames 
[MTU=9014 on the Windows side (includes IP headers) , 9000 on the Linux side 
(doesn't include the headers], I am getting about half the throughput that I get 
when I set both NICs to use the standard MTU of 1514/1500. I see the same 
behavior even if I take the switch out of the system and connect the Windows XP and 
Linux machines directly to each other (crossover cable not required for 
computer-to-computer connection with these NICs -- and by the way all of my cables 
are CAT6). 

On the Linux side, I am using Samba 3.0.0 on Mandrake Linux 9.2 with all of 
Mandrake's current updates -- kernel = 2.4.22-21enterprisemdk. The Linux 
machine is a P4-3.06 Ghz with 1 GB of RAM -- running in hyperthreading mode. 

I am wondering if any of the Samba socket options settings like tcp_nodelay, 
so_sndbuf=8192 or so_rcvbuf=8192 are affecting my throughput -- particularly 
when I am using Jumbo Frames? And are there any other Samba settings that might 
be interacting in a negative way with my TCP/IP and NIC driver settings that 
are causing me to get lower throughput with Jumbo Frames instead of higher 
throughput (which is what I am told I should be getting). 

Any guidance would be appreciated. I have purchased "The Official Samba 3 
HOW-TO and Reference Guide" but it really isn't very helpful when it comes to 
understanding how to tune these options and how various socket options settings 
interact with other network settings and hardware. 

Andy Liebman
Resolute Films
119 Braintree Street, Suite 410
Boston, MA 02134

Tel: 617-782-0479
Cell: 617-308-0488
Fax: 617-782-1071