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I'm having a strange problem on my mac pro (first 8-core) where my network speed is dreadfully slow when connected with Ethernet. Internet connections are about 10% of maximum speed and computer to computer connections are similarly crippled. If I upload to net I should have 220kb/s but often only see around 20. If i disconnect the Ethernet and use the wireless connection it goes to full speed. If I change from Ethernet port one to two or other way around it often starts out with maximum speed before slowing down. I thought it was my router, but it does the same with a connection directly to another computer. I have searched the net but not found any answer. Any help would be greatly appreciated! I move a lot of large files between local computers, so it would be a huge advantage to be able to use the Ethernet instead of wi-fi. I found this that seems to be roughly same problem: but I cant figure out how to use iperf as I'm useless with terminal.. Any help on this one? Thanks GT

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Need more info Have you always used wireless, and are just trying wired networking for the first time? If you've used wired before, did it just recently slow down? What's changed lately - new computer, new version of OSX? – stewartwb Sep 24 '10 at 14:30

Have you popped into activity monitor and clicked on the network tab to see how much information you are pushing when your computer is at idle?

When is the last time you did a complete wipe and reinstall?

Is it still under some kind of warranty either with AppleCare or some third party incase that the motherboard might be at fault? This is the last thing should be considered; however, you need to give a little more background on the computer, its' use, if you tried it on another network, etc?

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Hi Braden Thanks for you answer. I haven't done a clean wipe for about one and a half year. No waranty or applecare left i think. – GTurban Sep 26 '10 at 19:43
no heavy traffic when connection is idle. I have tried connecting directly to the laptop or via my hub. Both ways seem to have the same issue.. – GTurban Sep 26 '10 at 19:45

You said

If I change from Ethernet port one to two or other way around it often starts out with maximum speed before slowing down. I thought it was my router, but it does the same with a connection directly to another computer.

It sounds like you have two Gigabit-capable machines connected directly with a cable, and that a file copy starts out fast but quickly slows down.

I suspect that your target machine is having trouble saving data to the hard drive as fast as the source machine can deliver it. The speed is good at first, because the target machine uses RAM to cache the transfer. But with a large file and Gigabit transfer speeds, the RAM cache is quickly filled, and the transfer speed drops to match the speed at which the target system can save data to its hard drive.

I'd like to know the details on the source and target computers: what hard drives are installed, how are they connected, etc.

Servers typically use RAID to gang together many individual disks and increase disk performance (and provide fault tolerance). They also typically have very fast disk controllers customized for RAID, and large memory caches (with battery backup) to buffer file I/O operations. That is one reason that a good server costs many times as much as a good desktop.

Now, you also mention concern about the % of maximum throughput for each connection type. Of course, Gigabit connections are more likely to run well below the theoretical maximum shown in the performance monitoring tools, since so many devices have trouble keeping up with them. A wireless transfer is usually limited to 54Mbps, so a full-bore file transfer is more likely to stay close to 50-70% utilization on these charts. Even so, the actual throughput of bytes / sec should be either identical or faster over a wired Gigabit connection.

If the Gigabit transfer is actually slower (bytes/sec) than wireless, I suppose you might have a bad piece of hardware, a bad cable, a bad driver, or bad TCP/IP settings.

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Hi Stewartwb, Thanks for your time! At home I have a macpro (2006 8core) with two ethernet ports. one mac mini, and one macbook pro. They are normally connected with a gigabit-netgear hub, which is then connected to a wireless N-capable router. So all those machines are gigabit. If I start copying a file from the mac pro to the laptop or mac mini, the transfer starts out fast, but then slows down to roughly 1/10 of gigabit speed. If I swap the ethernet ports the transfer speeds up again. – GTurban Sep 26 '10 at 19:28
Also when I upload to internet, (dropbox) the transfer starts at full speed (I have a 2Mb upload) then slows down to around 20-40 KB/s... The same speed throttle happens if I connect the mac pro directly to a different computer with ethernet cable. The wireless connection is faster and more stable than ethernet. I had the laptop connected and backed up files whilst shooting tethered. the first batch of files went full speed, the later it started slowing down again. I'm thinking that there is some network configuration that is wrong.. – GTurban Sep 26 '10 at 19:38
I'm thinking it might be settings that are wrong, but have not found how to correct it. As sometimes I can get a whole batch of files (around 5GB) transfered at full speed.. – GTurban Sep 26 '10 at 19:41

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