Re: Tweaking TCP windowsize
Re: Tweaking TCP windowsize
- Subject: Re: Tweaking TCP windowsize
- From: Brandon Becker <email@hidden>
- Date: Thu, 23 Jun 2011 00:32:45 -0800
Hi Andreas,
You mention trying to set a 6M window size, but the command you're using attempts to set a 6G window. How do you know that making the window size 100 times bigger will also make network throughput 100 times faster?
I can't answer your questions and have very little experience tuning network performance, but I am very interested in watching this discussion.
Brandon Becker
Macs in Alaska LLC
On Jun 22, 2011, at 10:38 PM, Andreas Fink wrote:
> Hello,
>
> We run a datacenter in Iceland and as such we are transferring lots of data from central europe to/from Iceland.
> We realized that we never get over 10Mbps of speed while we have a dedicated point to point 1Gbps link in between.
>
> The problem is that filetransfers over TCP get slowed down by the window size which defaults to 64k. As there is 50ms delay between the sites, the window size does slam the breaks on the speed.
>
>
> I now want to change the default send window size to 6M so it would give us one full gigabit. However setting it with
>
> sysctl -w net.inet.tcp.sendspace=6442450944
>
> results in
>
> sysctl: net.inet.tcp.sendspace: Result too large
>
>
> which raises the following questions:
> a) what is the maximum value in the standard kernel?
> b) how can it be increased
>
> And can the window size not be dynamically expanded once its hit?
>
> I think in todays world 64k is way too low. A lot of destinations are 150ms delays away, simply by the fact they are at the other side of the planet. And speeds above 10Mbps for home users are very common while in the datacenters 1Gbps is common and everyone moves to 10GBps.
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