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Gigabit Running at <20 Mbps

Last response: in Networking
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March 21, 2010 3:37:38 PM

Hi all,

First off, I'd like to thank the members of these forums for helping me with a load of previous issues. I hope that you guys can help me with this strange one, for which I have not been able to find a solution.

I recently upgraded a small business network (15 computers) to use a 16-port gigabit switch. For some reason, the connection between certain computers to each other cannot reach gigabit speeds. I'm not one of those guys complaining about my gigabit network not being much faster than an old fast-ethernet network; this is an entirely different situation. Here's the scenario

Take for example 4 machines: Computer1, Computer2, ServerA and ServerB. The computers are running xp pro on more-than-gigabit-capable machines (core 2 duos, 4gb ram, sataII 7k drives), as are the servers (quad-core xeons, 8gb ram, sas 15k drives).

If I sit at Computer1 (with NIC set to either Auto-Negotiate or 1000fd), and copy a file from ServerA (Auto-Neg or 1000fd), I can only get speeds at 15mbits max. But if I set Computer1 to 100fd manually, the speed is around 80mbits. Copying a file from Computer1 to ServerA runs at full gigabit speeds. And if I sit at ServerA and copy a file onto Computer1, it can run at full gigabit speeds.

What makes it stranger is that the connection between Computer1 and ServerB runs fine at full gigabit, as does the connection between ServerA and ServerB. But the connection between Computer2 and ServerA has the same problems as the connection between Computer1 and ServerA, which are somewhat mediated by a manual 100fd setting.

I know this sounds pretty complicated, so if I can provide any additional clarification please let me know.

Any input would be greatly appreciated. Thanks for looking!

More about : gigabit running mbps

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March 21, 2010 9:11:22 PM

Gigabit usually is set to Auto. The issue that you describe is what happens when the NIC and the switch don't negotiate properly. If all systems have a Gigabit NIC, then set all ports on the switch to Gigabit (presuming that you use a manageable switch) and the NIC to Auto.
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March 21, 2010 11:02:50 PM

I think I solved it, and for those who may come across this in the future:

Updating the drivers (duhh idiot move) on the slow server seemed to fix things. The previous drivers had dated back to 2003, and updating to the new version has everything running smoothly.

One of the older computers that still uses IDE drives cannot achieve consistent speeds, which is to be expected from its slow hard-drive. The network speed has many spikes and valleys...probably normal?
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March 21, 2010 11:51:34 PM

Quote:
The network speed has many spikes and valleys...probably normal?
Unless you copy very large files, it's normal.
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March 22, 2010 12:45:03 AM

i was testing with a 400mb avi file. does that count as very large?
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March 22, 2010 12:49:40 AM

Yes, but unless you have very fast RAID subsystems, Gigabit is faster than the hard disks. The test is valid from several PCs to a high performance server.
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March 22, 2010 1:10:34 AM

Best answer selected by tshaw.
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