[Samba] About SOCKET options

Benjamin Weber shawk at gmx.net
Thu Sep 26 12:48:01 GMT 2002

Ok, as some of you read I was the guy who experimented with SOCKET options.

In my last post, where I figured that I needed to use the right syntax I
found out that SO_SNDBUF=4096 and SO_RCVBUF=4096 worked way better than with
8192 as value. Today I verified this behavior.

I used SO_SNDBUF=4096 and SO_RCVBUF=4096 and copied a 780 MB file from
Windows to Linux. ETA of Windows was 4 mins and it did indeed happen within
4 mins (13:58-14:02).

I switched to SO_SNDBUF=8192 and SO_RCVBUF=8192, rebooted (just to be sure),
and copied the same file again. ETA of Windows started at 45 mins and rose
up to 101 mins. I waited for 2 mins and it was copying the hell slow. So I
assume it would indeed take around 80-100 mins to copy the same file. I

Swichted back to 4096 et voila, was at 4 mins again.

Checking the Internet for socket options it does say that windows SO_RCVBUF
and SO_SNDBUF are at 16k on default. You can increase the number but there
is a point where the results do get worse again, e.g. picking too high or
too low a number. I assume the same is true for the Linux system, since the
socket stuff belongs to the network protocol and is not OS dependant.

My physical network configuration is:

Windows XP on an AMD XP2000+
Intel Ethernet Express 100b

Debian Linux on AMD Athlon 650
3Com 905C-TX

on a switched 100 MBit Network. (via a hardware SMC Barricade broadband

Can anyone explain this weird behavior to me? Especially since almost all
internet sites recommend 8192 nowadays and not 4096. Why should 4096 be
faster for me? Am I a rare case (since everyone seems to recommend 8192)?

Benjamin Weber

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