Hi,
I have an application pushing data on long WAN links.
The application runs on RHEL4.
It is not able to utilise the complete available bandwidth.
I was told that kernel needs to be tuned for "long fat" links, so that the system starts utilising complete available bandwidth.
I found a link "http://www.kernelfaq.com/2007/07/tcp-tuning-sysctls.html", however it is on FreeBSD.
Does any one have info on this.
Regards
Mahen

Are you running GigE or fast Ethernet? How fast are you actually moving data? With fast Ethernet anything over about 9.5MB/sec is probably the best you are going to get without a ton of work. You can use channel bonding but by the time you get all the extra equipment and get it working you are usually better off(and cheaper) just moving to GigE. On GigE you should be seeing 95MB/sec(assuming your hard drives can handle that fast).

Hi ,
I am sorry for not giving complete info.
The OS is RHEL 4 with 2.6.9 kernel. The auto tuning is set to on.

The application runs on a Dell 2950 with GigE network, however bonding is not supported by this app.

The available pipe is 135 MBps, unfortunately the application is using only 6 Mbps, ealier.

www.psc.edu/networking/projects/tcptune/#Linux - is the link we followed.

Today our manager has made some changes in the propreietry application and we have seen a good performance change.

We changed the default tcp_wmem on source and tcp_rmem on destination, tested the params with iperf (transmitting 1 MB packets).

now its going till 2MBps :-), i believe with your suggestions we can get more.



Any insight on this? do we need additional info?

mahen

dpnctl

Just to be sure. Mbps is the standard for transmission rates(Meba bit per second).Mbps does not equal MBps(factor of eight difference). For instance fast ethernet is 100Mbps, not 100MBps(Mega Byte per second).

My guess is that your pipe is actually 135Mbps.

Bonding would be at the OS level not at the application, which is irrelevant since you are on GigE.

For the transmit levels to be that low you almost have to be defaulting to fast Ethernet or even base 10. In order for GigE to work the entire path the data follow HAS to be GigE equipment. Every cable, switch, router, and machine that the data goes through has to be GigE. Start by checking with ethtool on both ends to make sure they are actually running GigE.

Note in this example I have a GigE card but I am hooked up to a Fast Ethernet device. Therefore it drops back to the fast Ethernet speed.

Now for the bad news, all that tells us about is the connection between the machine and the first device it connects to (switch, router, machine, etc). Even if I had been running at GigE on this first hop, the next hop might only be fast Ethernet. The only way I could know this (from my machine) was by the fact that my throughput was low(like yours is). Even if every hop on the path is GigE equipment you could have a failure anywhere along the line. Cables (particularly with homemade ends) are notorious for this. The other thing to look out for is if somebody ran the cable too long. It may only be 100meters(GigE limit) from point A to point B but that is irrelevant, it is the actual length of the cable being used. IT guys are notorious for using two 75 meter cables with a (passive) connector and then wonder why they are having intermittent issues.

Just a few things to check off the top of my head.