How to increase transfer speed on fat long pipe?

Question

I have a log pipe between two facilities (gigiabit circuit with RTT latency of 17ms). When doing system-to-system file transfer (file sharing, rsync, ftp, sftp) I'm hitting maximum speed of approx 30 megabits, which is less than I expect.

OS: Windows XP and Windows Server 2003

Here is what I did:

1. Modified registry setting as follows:

   [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"Tcp1323Opts"=dword:00000003
"GlobalMaxTcpWindowSize"=dword:00206cc8
"TcpWindowSize"=dword:00206cc8
"SackOpts"=dword:00000001

2. iperf shows near ideal 900 megabit transfers, so pipe can handle it.

I understand, that using some kind of UDP layer can help me, but here this isn't an option.

thanks.

Answer 1

I would try messing with your MTU as well. For systems that use a PPPoE connection, an MTU of 1492 (1500 being default) works better than anything else. If all the networking gear supports jumbo frames, you can try pushing it all the way up to 9000. It should be located at:

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces

Also, a Link about tweaking for network speed

Answer 2

Independent of the OS being used, TCP settings tremendously affect the perceived maximum throughput. E.g. the chosen congestion avoidance algorithm greatly affects it (especially when using fat pipes). Others can be seen here: http://support.microsoft.com/kb/224829

Note that TCP settings only affect upstream traffic.