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I transfer large files between two of my servers one in the US and the other in the Netherlands and I'm wondering if there are any tweaks I can apply that will increase the speed of a transatlantic tcp transfer (ftp or http).

Right now I'm running on the defaults of Ubuntu natty except for rmem_max and wmem_max which I increased according to a BDP calculator.

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You're on the right way and you'll have to tune on your own; There no generic answer here. But before you really start to tune do yourself a favor and check the traffic with something like Wireshark to see where the problem might be. Is it windows size related, are there many retransmissions, would multiple flows help, etc.

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is there a wireshark alternative for CLI use? I'm running on headless machines. –  incognito2 Oct 10 '11 at 16:39
    
@incognito2 Use tcpdump to do the capture, then you can import that file into Wireshark for analysis. –  EEAA Oct 10 '11 at 16:53
    
I did a capture on a transfer between my home machine and a server in the EU. What I got was a window size of 115 and a window scaling factor of 115 for a total window size of 14720. I'm guessing this is my problem but how do I fix this? –  incognito2 Oct 10 '11 at 17:08
    
Wireshark has it's own cli version called 'tshark'. Whats your RTT and bandwidth? –  pfo Oct 11 '11 at 15:41
    
140ms, bandwidth is 100mbit –  incognito2 Oct 14 '11 at 23:39

Depending on the sort of data (especially whether it's encrypted already), your budget and space in each datacentre, you may want to look at WAN optimisation. We have extensively used Riverbed, but other options (including software-based) do exist.

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