We just got a new dedicated 1 gigabit server running IIS.

The CPU is 15% or less, the RAM (4 GB total) has 3 GB unused...

We are pushing 110 mbits per second... Speeds are really slow.. And, if fact, here's how it happens: We connect, and then the speeds are really fast, and quickly decline to 40 kBps or less.

What's going on? It seems the server just wont go above 120 mbits per second.

The files are all very large. 50 MB to 500 MB... Could this be a factor?

Again, CPU, RAM, UI responsiveness when accessing remotely all seem fine.

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    How are you measuring speed here? Where are you testing from? What is in between? – dunxd Oct 15 '10 at 22:53

Slow performance for large file downloads could indicate that your server's NIC didn't auto-negotiate properly with the switch. Check the settings to make sure that it's running at 1000Mbps and full duplex. You may want to have your provider verify the switch port settings as well.

I don't see many problems with servers auto-negotiating with switches at gigabit speeds these days, but if you suspect negotiation problems, try turning off auto-negotiate and forcing 1000/full (you'll need your provider to do the same on their end).

While you're working with your provider, you could also double-check your MTU settings against what they recommend that you use.

If all else fails, fire up Wireshark on both ends and capture some packets to see what's going on with the TCP stream during your slow downloads.


You might also take a look at your storage to ensure it is not the actual bottleneck. The initial quick performance may be the result of a cache and then the eventual speeds may actually reflect the performance of the storage system when it depletes what has been cached.

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