networking - Not getting gigbit from a gigabit link?

I just upgraded my LAN to gigabit. This is what netperf has to say about things.

Before:

marcus@lt:~$ netperf -H 192.168.1.1
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 (192.168.1.1) 
port 0 AF_INET : demo
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 87380  16384  16384    10.02      94.13   

After:

marcus@lt:~$ netperf -H 192.168.1.1
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 (192.168.1.1) port 0 AF_INET : demo
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 87380  16384  16384    10.01     339.15   

Only 340 Mbps? What's up with that?

Background info: I'm connecting through a gigabit switch to a sheevaplug. I have Cat5e wiring in the walls and the run is maybe 30 feet. If you're not familiar with netperf, it has a tendency to give very stable results and never lie.

Answer

Check out this thread. One of the contributors (Frennzy) outlines this very nicely. I'll quote:

The "real" speed of gigabit ethernet is...

1Gbps.

That is to say, it will transfer bits at the rate of 1 billion per second.

How much data throughput you get is related to various and sundry factors:

NIC connection to system (PCI vs PCIe vs Northbridge, etc).

HDD throughput.

Bus contention.

Layer 3/4 protocol and associated overhead.

Application efficiency (FTP vs. SMB/CIFS, etc)

Frame size.

Packet size distribution (as relates to total throughput efficiency)

Compression (hardware and software).

Buffer contention, windowing, etc.

Network infrastructure capacity and architecture (number of ports, backplane capacity, contention, etc)

In short, you won't really know, until you test it. NetCPS is a good tool for this, as are many others.

And this, later in the thread (my highlighting):

Stop thinking like this. Stop it now. All of you.

As much as you would like to figure out kilo-or mega BYTE per second transfer, the fact is that it is variable, even when network speed remains constant. Network "speed" (bits per second) is absolute. Network throughput (actual payload data per second) is not.

To the OP: will you, in general, see faster data transfers when switching from 100Mbps to 1000Mbps? Almost definitely. Will it be anywhere close to the theoretical maximum? No. Will it be worth it? That's for you to decide.

If you want to talk about network speeds, talk about network speeds. If you want to talk about data throughput, talk about data throughput. The two are not tied together in a 1-1 fashion.