[GLLUG] Transferring high volumes of data.

[Andy Smith]

Hi JLMS,

On Wed, Jun 11, 2014 at 08:08:40PM +0100, JLMS wrote:
> I see almost 5ms when I ping between hosts (TCP or UDP are  pretty similar).

Are you sure about that? 5ms is a pretty low latency circuit and if
you can't achieve significant throughput at that latency then I'd
start to suspect the infrastructure.

Having said that, this calculator does suggest that you should
expect around 204Mbit/sec as a maximum for a TCP stream at 5ms with
default Linux window size of 128kByte:

    http://www.switch.ch/network/tools/tcp_throughput/index.html?do+new+calculation=do+new+calculation

It suggests that you need a TCP window of 640kByte to achieve
1Gbit/s at that latency, so you might want to try playing with the
figures in:

    /proc/sys/net/core/*mem_max

Here's some more info:

    http://www.cyberciti.biz/faq/linux-tcp-tuning/

Cheers,
Andy

-- 
http://bitfolk.com/ -- No-nonsense VPS hosting