April 9th, 2007

  • evan

network bottleneck

I transferred some big files from my laptop to my roommate's NAS box last night and it was pretty slow. Lazyweb, please help me diagnose!

Over a gigabit ethernet cable the transfer (via rsync's protocol) went at about 1.2mb/sec. My machine is a Thinkpad T41p. I think it's got gigabit ethernet 'cause that's what I read online, but that transfer speed isn't even 100mbit.

Repro: plugging a Mac laptop into the same cable managed to read files at maybe 30mb/sec. (Memory hazy but writing went at maybe 10-15mb/sec.)

Local hardware: curiously, iostat showed my disk only reading in the tens of kbs per second, so I guess that's broken. Catting another big file to /dev/null as it transferred didn't slow it down. CPU was mostly idle.

Network configuration: mii-diag (is that for all cards or just some specific one?) indicated 100mbit, full-duplex but it doesn't seem to know about gigabit so maybe it's confused. (And as pointed out, we were getting closer to 10mbit.) ethtool claimed a "speed" of 1000mbit but it's unclear whether that was the actual wire speed or just a setting to let you cap the speed.

What am I missing?

(My suspicion now that I've written that is that maybe it was using the wireless accidentally? But network manager did all of the wireless-disconnection, ethernet-DHCPing stuff when I plugged the cable in so I didn't think to verify...)