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SFP+ Connection bad performance

Konstantin Krolikov
Last Modified: 2019-12-17
There is existed 2 servers which located in same subnet.

Server 1
Name: Storage-01
Type: Dell T430
Network card: Intel(R) 10G 2P X520 Adapter (10GB) (1GB)

Server 2
Name: Hyper-V-01
Type: Dell T430
Network card: Intel(R) 10G 2P X520 Adapter (10GB) (1GB)

They both connected over Dell brand DAC cable SFP+ of 5 meters to Dell switch N1548 to SFP+ ports.

But when i'm copying file or executing iperf between, performance are really bad.
About 16 MBytes (136Mbits).

When i'm doing copy of any file from any Workstation i do receive performance of 113MB as expected. Like 1GB connection of workstation that connected to same Dell switch.

I was thinking that i have switch issues or cables. I took brand new cable and connected peer to peer and configured them in different subnet like and and did same test but received almost same result.
About 17.2 MBytes (150Mbits)

Maybe some configuration is wrong ?
Maybe i have issues with network card ?
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