Got Gig?

A couple weeks ago I made the big jump to GigE at home. Why have gigabit ethernet at home? Why not! The first step to this Geek Fest was to figure out what was needed. Chris Tersteeg gave me a quick download on the marketplace (what is it with him and this type of information?!) and I did some research on my own as well. To be elite you really need to have jumbo frame support on your gigabit gear.

What is jumbo frame support you ask? Well, in a normal or fast ethernet network your frame size is pretty small, 1,500 bytes. So everything you send is chunked down into frames of 1,500 bytes. To send 1MB of data requires 700 frames. Well, with gigabit you are going to break things down into a lot of frames. To make life more manageable you can enable jumbo frames. This allows you to increase your frame size to values like 9,000 bytes. This makes that 1MB of data only require 117 frames! You can do the math, 1/6th the number of frames and hence fewer interrupts and the like on the network. Theoretically, faster throughput (hmmm, or not, see iperf results below).

I settled on the SMC 8508T which brings 8 ports of full gigabit and support for jumbo frames. This is the only switch in the sub-$150 range with jumbo frames. I then opted for the high-end and went with the Intel Pro/1000MT gigabit cards. These also support jumbo frames (need that on both the server and the workstation) and have good drivers.

One of the fun things about gigabit is that you don't have to worry about duplex. It's just handled automagically. Other than that, everything is pretty much the same.

So, how does it perform? The following tests were all done using iperf.

Configuration Test 1 Test 2
No Jumbo Frames Up 515 Mbps / Down 611 Mbps Up 510 Mbps / Down 612 Mbps
4,088 bytes Jumbo Frames Up 499 Mbps / Down 650 Mbps Up 525 Mbps / Down 704 Mbps
9,014 bytes Jumbo Frames Up 596 Mbps / Down 540 Mbps Up 599 Mbps / Down 506 Mbps

Note, the Intel Pro/1000MT supports frame sizes up to 16,000 bytes! However, when I used these iperf kept on crashing on me when I did the test. Note, the SMC 8508T only supports up to 9000 bytes frames so not sure what happens when you try to send frames larger than the switch supports.

The performance is a little puzzling. Hard to identify any real patterns, and the asymmetry makes no sense. To add even more confusion to it, the performance advantage flip-flops between 4,088 byte frames and 9,014 byte frames. I've left my system using 4,088 byte frames for now, but haven't had the time to really dig into what is going on on the wire here.

The end result is a blazing fast home network backbone. The realistic application of this is that network disk performance is almost as fast as local disk performance. So doing image manipulaton of MP3 management over the network is much more realistic.

All of this performance, and the total cost to do this Geek Fest was around $220. It's amazing to me how far your dollar goes when buying gear these days!

The next Geek Fest will be the installation of over a terabyte of disk in the home server. Stay tuned!