Iperf speed confusion

[Dalma]

I have been trying to track down a CIFS speed issue so I loaded Iperf on my windows 8 client last night.

My windows 8 client is a Microsoft surface pro 2 and I'm using a USB to Gigabit adapter.

My freenas box is a new build with a Asrock Motherboard with Intel nics on it. My switch is a Gigabit switch. All devices report running at Gigabit speed full duplex.

When I test with Iperf between my windows client and freenas box I see about 500 mbs.

I also have a Ubuntu server on my lan and when I test between my windows client and Ubuntu box I see almost a full Gigabit. When I test between Ubuntu box and freenas I see almost full Gigabit as well. The only combination with the speed issue is the windows to freenas so I'm a bit stumped.

 

[krikboh]

The USB adapter is most likely the issue. Is this even a USB 3.0 adapter?


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[Dalma]

It is a usb3 to Gigabit adapter. I also believe that this is likely part of the problem but can't explain why I see twice the speed on the client to ubuntu server test as I do on the client to freenas test.

 

[zambanini]

whoch tcp windows size did you use with iperf on each size?

 

[Dalma]

I ran with the default of 64kb in each case.

 

[zambanini]

up and down give you the same result?

 

[Dalma]

I didn't think to try in both directions. I will do so later today when I have access and will report back.

 

[Dalma]

I retried by tests again last night and could not duplicate the results from the previous day.

Now in each case involving the Surface Pro 2 client transmitting in any direction shows about 500mbs. I guess the issue is in fact related to the USB Nic adapter. All communications between the Freenas and a Ubuntu host on my network were at full 1000mbs speed well high 900's anyway.

I want to thank each of you that took time to comment.