FTP transfer getting slower.

hi all,

I've setup a PXE+G4U server for 45PCs.. the server run on Athlon
1700,512 MB ram and RAID-0 IDE HD and 100baseT nic(changed to
gigabit), the client is using nvidia integrated gigabit nic. And it's
using NetBSD (pxeboot_ia32.bin) kernel and vsftpd as FTP server.

When 4 clients started to receive image file from server, it can get
6-7MB/sec at starting (which I think is too slow), and getting slower
until 2-3MB/sec after 40-50minutes .. so i thought is 100BaseT
problem, I then slot in a gigabit NIC. I tot it will give me at least
10X 2-3MB/sec, but too bad it only give me 8-7MB/sec at first, and
finally drop to 2-3MB/sec after 40-50minutes. It's a big problem to
transfer 149GB across the network with 2-3MB/sec.. So it come out
restore 1 client with more than 12 HOURS!!..

I'm browsing around the google but dun find any clue yet. Hopefully
someone onboard can help me on this, or point me which direction i
should go into for debug.

Thanks.
Max.