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Checking Google, 100mbps (Fast Ethernet, wired) is ~12MiB/s but in reality, transferring a file over the network (home LAN) is only ~1.5MiB/s. Why might that be?

I am on Ubuntu 11.10 transferring to Windows 7 (the other direction, copy, gives a similar speed).

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How exactly are you measuring? How are the two machines connected to each other? (Through what other device(s)?) – David Schwartz Dec 18 '11 at 5:28
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Other things to consider that would affect speed, the CAT rating of the cables and anti-virus. When I switched from CAT5 to 5e to 6, each step I got a speed increase. When I rerouted my cables away from power cables the speed was more consistently fast. When I disabled my AV on Windows, that helped speed the transfer. Using SSDs, helps network transfer. Getting the max speed out of your network speed is still kind of voodoo, you almost have to try different things. – Scott McClenning Dec 18 '11 at 7:22
@DavidSchwartz, computers are connected by a fast ethernet switch, which is connected to a router/modem for internet access. A computer is connected through a powerline device, but I tried transferring between 2 "non-powerline" device, resulting in similar speeds – Jiew Meng Dec 18 '11 at 12:13
@ScottMcClenning, maybe its because my switch is close to wires ... hmmm .... – Jiew Meng Dec 18 '11 at 12:14
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3 Answers

up vote 3 down vote

Use a tool like IPerf to really see what your TCP throughput is with a well-optimized TCP app. IPerf will also tell you what your default TCP window size is, which might be telling.

Check to make sure all of your Ethernet cables are properly wired. Many people (and cable testers) check for pinout correctness without checking to make sure the conductors from each pin is twisted together with the conductor from the correct paired pin (Hint: 1&2, 3&6).

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up vote 2 down vote

It's possibly due to interface errors, so check for that (specifically for speed/duplex).

It could also be that the router/switch/hub doesn't have enough juice, so try a crossover connection just to make sure its not that.

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how do I check for interface errors? I am using Ubuntu, the computer I an transfering to is Windows 7 – Jiew Meng Dec 18 '11 at 12:15
ifconfig will tell you if you have any collisions – alexus Dec 19 '11 at 16:14
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up vote 0 down vote

The bottleneck is probably disk I/O, or something other than the ethernet. The something could be the processor, latency, the modem, the network card, the other network card, or evne something that is more system specific.

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Just checked again, disk write is ~100MB/s locally – Jiew Meng Dec 18 '11 at 4:08
"or something other" is extremely vague.. Could you expand more? – Simon Sheehan Dec 18 '11 at 4:39
@SimonSheehan done. – soandos Dec 18 '11 at 5:09
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I still find it extremely vague as you don't really provide any way to help speed it up or to find why. – Simon Sheehan Dec 18 '11 at 13:34
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