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I have a problem: sending small files (16MB) works with at most ~ 2MB/s speed. While on larger files, 16MB/s is easily achievable.

When I was checking details, it looks that speed of transfers starts very low - ~ 200KB/s, and then increases, but 16MB is too small to reach big enough speed.

I read about it, and it looks like it is "Slow Start" technique. I did find some pages on the google on how to disable it, but nothing that I tried so far seems to help.

The problem is that I need to send, very often, relatively small files, and the network link is fast enough to handle it (16MB/s gives me 1 second to transfer the file, which is perfectly OK for me), but the Slow Start thing is causing the file to transfer in ~ 8 seconds which is unacceptable.

The question basically boils down to: is there any way to disable slow start, or at the very least - make it start with speeds like 4MB/s, and not 200KB/s?

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closed as not constructive by DerfK, mgorven, mdpc, Khaled, Ward Feb 28 '13 at 14:51

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.If this question can be reworded to fit the rules in the help center, please edit the question.… – Henry S. Feb 27 '13 at 20:43
The question got closed as not constructive, but I don't understand it. It is constructive - I'm looking for a way to disable slow start or reconfigure it ? – user13185 Feb 28 '13 at 23:19

1 Answer 1

The ability to change the inital window size was backported beginning with RHEL 5.8 and RHEL 6.3.

So, first, upgrade your system, and then you specify the cwnd in your ip route. For instance:

ip route change default via dev eth0 initcwnd 10 rtt 2500

The rtt specification is needed to work around a bug in the EL5 backport where initcwnd would not be applied in all cases. (The bug is not present in the EL6 backport.) The example given is for WAN links; it should be much smaller (e.g. 100) for a LAN route.

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