Maximum transfer speeds on LAN lower than LAN capabilities

R4ABigman · Post by **R4ABigman** » 2005-11-16 11:13

Hi there

I have recently been involved in setting up a DC hub for the use at a LAN event. The LAN equipment used allowed gigabit transfers to occur, so the maximum throughput possible should be however fast your harddrives can handle data (as the network runs faster than they do), which from plenty of past experience is around 30-40MBytes/s for myself.

When the network wasn't busy we were testing DC. Having people upload from my machine the throughput would always level off at around 7MBytes/s no matter how many people got different files. I also noticed my computer practically grind to a halt. On inspection DC was using 100% of my CPU. Stop the uploads, and the CPU usage dropped back to negliable levels. Other people were experiencing the same issues, though with faster computers their transfer speeds would be faster (up to around 12MBytes/s for the fastest machines we had).

Now considering standard Windows File Sharing will allow throughputs of up to 40MBytes/s we were keen to work out why DC was going horribly wrong for us. On searching through the options we found an option for "Enable Safe and Compressed Transfers" which was enabled. On disabling it, the CPU usage dropped to practically nothing during uploads and I was achieving upload speeds of around 15-20MBytes/s.

This solved one problem, but that was still only around half the speed I was expecting to achieve. I cannot work out why this is the case either, other than maybe DC cannot handle the kind of speeds on gigabit networks. I know it is primarily used for the internet, which is far slower.

The clients being used were actually BCDC++, simply for the option of bandwidth limiting when people wanted to play games. If anyone has any suggestions why the speeds seem so slow when using DC over LAN that would be fantastic.

All comments, suggestions etc are greatly appriciated.

Post by **GargoyleMT** » 2005-11-16 11:48

The bandwidth limiting code in BCDC++ can be inaccurate at high speeds, because of timer resolution. Disable the limiting and see if that improves things.

Otherwise, you found the primary piece of advice we have for LAN DC hubs and clients - disabling compressed transfers. Have you tried any of the generic TCP tweaking sites? I'm sure there are some that specialize in gigabit speeds. (at those speeds, enabling TCP checksum offloading may help too.)