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When I connect 2 PCs with each other through a 1GigE crossover cable and transfer large files (often larger than 1GB) through FTP, I often got transfer speed of around 70MB/s, which is likely limited by the hard drives and not by Ethernet's bandwidth.

I don't have a USB 3.0 device at hand, but we can safely assume that the limiting factor is still the hard drive's spinning speed (we aren't talking about SSDs here).

So, ceteris paribus, which protocol taxes the processor more (given the same transfer rate ?)

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While ultimately the computer's CPU is involved in the process, the reality is that it is so negligible, that it is irrelevant. Both USB and Ethernet have their own controller chips and do not rely on the CPU for instructions or processing power.

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This is not 100% correct. Some Ethernet chips may in fact rely on CPU to do some part of the processing and by that make an impact on the system performance. – AndrejaKo Sep 11 '11 at 17:51
Just today I noticed that transferring a bunch of files over my laptop's WiFi connection consumed a considerable amount of CPU (about 10%). Which although mean I could still easily saturate the connection, there's still quite a bit of overhead with networking. Although this was Wifi, So maybe my CPU was helping out in some of the encryption. – Kibbee Sep 11 '11 at 19:22
it really depends on your hardware. – Keltari Sep 11 '11 at 19:44

Over Gigabit ethernet the max you could ever get is 128MB/s, take into the fact of TCP error checking and the OS having to deal with the file move then you can sat that 70MB per second is about right not every bit sent over the network is the file itself there are a lot more mechanisms in place, Im guessing since your already getting over 66 that your on Sata 1 disks at least. So your bottleneck isn't your hard-drive.

Hard disks

ATA 33 = 33 MB/s

ATA 66 = 66 MB/s

Sata 1 = 187.5 MB/s

Sata 2 = 375 MB/s

Sata 3 = 750 MB/s

Your final question is a bit off topic of your opening but there both cpu un-intensive as there IO devices

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The SATA speeds you have mentioned are the interface speeds. Actual (consumer, non RAID) HDD's top out in the 70-100MBps range. – Akash Sep 11 '11 at 17:53
-1: Consumer hardrives are gonna be pushing 187.5 MB/s. – surfasb Sep 11 '11 at 19:11
You are vastly overstating the bandwidth of SATA. – Mr Alpha Sep 11 '11 at 19:36
There are the facts of the ATA and the SATA bus, and the fact that you mention RAID in it at all bewilders me, You still have the same disks in a raid array, yes in theory you can read faster in a stripe but the disk still reads at the same speed. – squarebear Sep 11 '11 at 19:37

Your harddrive is the limiting factor here at 70MB/s. Past the 100 MB/s range, other factors come into heavy play. How do you transfer the files? On the network, FTP is typically the fastest compared to SMB. For SMB, SMB 2.0 will knock the socks off earlier implementations. On the Windows side, that means you'll need Vista SP1/Server 2008 and above. On the Samba side, I don't know of any distros that use SMB 2.

Since there has been little benchmarking information on USB 3, I'll reserve judgement on which will be faster outside the 100MB/s range.

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