Channel bonding Gigabit Ethernet

[In-Su Yoon]

Hi, Glad to meet you.
I have an 8-node cluster and 3Com SuperStack Switch 4900 which supports Link Aggregation.
Each node has 512 MB SDRAM (133 Mhz) and Intel Server Board SDS2 with dual Pentium III 1.4 GHz.
Also It has two Intel 82544 (known as e1000) Gigabit Ethernet cards which use 64 bit/66 Mhz PCI bus.

I performed some experiments with NetPIPE benchmark under Linux kernel 2.4.19.
When I use one Gigabit Ethernet, the maximum bandwidth is approximately 863 Mbps.
But, When I use the channel bonding for two Gigabit Ethernets, the maximum bandwidth is approximately 650 Mbps.

How can I achieve the bandwidth of 1Gbps? What is a bottleneck for my channel bonding configuration?
Is channel bonding for Gigabit Ethernet useful?

But when I transfer bulk data of 400MBytes using FTP program, the bonding has better performance than one Gigabit Ethernet.

Thanks.