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I am having trouble getting my Gigabit network to work properly between my desktop computer and my Windows Home Server. When copying files to my server (connected through my switch), I am seeing file transfer speeds of below 10MB/s, sometimes even below 1MB/s.

The machine configurations are:


  • Intel Core 2 Quad Q6600
  • Windows 7 Ultimate x64
  • 2x WD Green 1TB drives in striped RAID
  • 4GB RAM
  • AB9 QuadGT motherboard
  • Realtek RTL8810SC network adapter

Windows Home Server

  • AMD Athlon 64 X2
  • 4GB RAM
  • 6x WD Green 1,5TB drives in storage pool
  • Gigabyte GA-MA78GM-S2H motherboard
  • Realtek 8111C network adapter


dLink Green DGS-1008D 8-port

Both machines report being connected at 1Gbps. The switch lights up with green lights for those two ports, indicating 1Gbps.

When connecting the machines through the switch, I am seeing insanely low speeds from WHS to the desktop measured with iperf: 10Kbits/sec (WHS is running iperf -c, desktop is iperf -s). Using iperf the other way (WHS is iperf -s, desktop iperf -c) speeds are also bad (~20Mbits/sec).

Connecting the machines directly with a patch cable, I see much higher speeds when connecting from desktop to WHS (~300 Mbits/sec), but still around 10Kbits/sec when connecting from WHS to the desktop. File transfer speeds are also much quicker (both directions).

Log from desktop for iperf connection from WHS (through switch):

C:\temp>iperf -s
Server listening on TCP port 5001
TCP window size: 8.00 KByte (default)
[248] local port 5001 connected with port 3227
[ ID] Interval       Transfer     Bandwidth
[248]  0.0-18.5 sec  24.0 KBytes  10.6 Kbits/sec

Log from desktop for iperf connection to WHS (through switch):

C:\temp>iperf -c
Client connecting to, TCP port 5001
TCP window size: 8.00 KByte (default)
[148] local port 57012 connected with port 5001
[ ID] Interval       Transfer     Bandwidth
[148]  0.0-10.3 sec  28.5 MBytes  23.3 Mbits/sec

What is going on here?

Unfortunately I don't have any other gigabit-capable devices to try with.

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Never heard of iperf before, thanks for pointing that out – TheLQ Sep 5 '10 at 16:29
up vote 1 down vote accepted

I find it very odd that the speeds change so much when you change the server with iperf. I would expect the same performance in both directions. This looks like something hard to find. Try these options:

  1. Upgrade the BIOS and the network drivers. Download the latest version from the vendor site.
  2. Check the settings of your virus scanner. Disable it (and all other unimportant processes).
  3. Check for a virus.
  4. Make sure that duplex mode is active (no idea how to do that on Windows; on Linux, it's ethtool).
  5. Get a new cable; maybe a strand is bent/broken/flacky.
  6. Replace the oldest component with a newer one. Gigabit Ethernet should "just work" but there are combinations of devices which fail because of something odd.
  7. Get a new Gigabit network card. They are cheap and easy to install. Maybe one of the network ports if defective (so you can receive with high speed but can't send).
share|improve this answer
I replaced both network cards with Intel cards, and everything works as it should. – Vegard Larsen Nov 15 '10 at 7:11

If you can, try connecting the server and desktop directly with a different category 6 cable and running tests.

To me it seems that the switch is making some problems on the way, but is not the main source of problems.

Make sure that on both desktop and server same settings are selected for network connection. This should have been set up automagically, but it doesn't hurt to check for yourself.

Take a look at duplex and speed on both interfaces. Also take a look at MTU size on both computers.

share|improve this answer

Are the WD Green drives EARS model? WHS doesn't play well with these - they have a new advanced format. there is extensive discussion on WHS boards.

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