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I have a simple computer networking question.

Gigabit connection, both computers have 500GB 7200rpm hard drives. One is core i7 860, and the other is Core 2 Duo 2.66Ghz. Both pretty fast computers.

When I hook up my desktop and laptop that are both running windows 7, with a crossover ethernet cable for a direct connection, why does the transfer start around 70-90 MB/s and then level off at 30 MB/s. I know the hard drives can handle more than that.

Why can't I get sustained high transfer rates?

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3 Answers

up vote 3 down vote accepted

Many factors can affect this.

  • Speed of the drive itself
  • Other programs accessing the drives at the same time
  • Where on the drive the data is located
  • Drive fragmentation
  • Number of files being transferred ( 1 huge file will go faster than 10000 tiny ones )
  • etc.

I can peak just a bit above 100mb/s on mine but it usually slows down and goes between 40 - 80mb/s after that depending on which drives and going to/from. I'm going between Win7 and Ubuntu.

On Windows7/Vista there's a built-in throttling mechanism.

Because multimedia programs require more resources, the Windows networking stack implements a throttling mechanism to restrict the processing of non-multimedia network traffic to 10 packets per millisecond.

The throttling will come into effect only when you are running multimedia programs that are time sensitive. However, this throttling mechanism can potentially cause a decrease in network performance during the active multimedia playback period. This decrease in performance is likely to occur only on high speed networks that are saturated to maximum capacity.

There are many things you can try. Its debatable as to how much of a performance boost you'll get. You could try this: http://support.microsoft.com/kb/948066

You can also see if enabling jumbo packets on both machines could help. Larger packets could help. This may or may not help.. Check out the link. http://www.codinghorror.com/blog/2009/03/the-promise-and-peril-of-jumbo-frames.html

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Thanks! I will check those links out! –  zm15 Jun 29 '10 at 19:06
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1000Mbps is the theoretical maximum speed of the gigabit ethernet. In actual usage there is overhead generated by the protocol. For example, FTP has much lower overhead than windows file sharing (SMB). In practice 30-40MB/s is pretty good numbers for windows file sharing.

Test with ramdisk if you are not sure whether the harddisk is the bottleneck. 30MB/s also resembles the maximum speed of harddisk connected via a USB interface (which it doesn't sound like the case to me)

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would it make a difference if I enabled Jumbo Frames on both PC's?? –  zm15 Jun 29 '10 at 18:39
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I'm not sure that those hard drives can sustain more than that...

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hmm, when i transfer/move various files on my desktop - i have 3 drives internally which are comparable to the laptop hard drive - I can usually get sustained rates of at least 50+ MB/s –  zm15 Jun 29 '10 at 18:32
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