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vSwitch Local Speed

A client told me today he thought he was having poor backup performance over a virtual network. But when he started debugging he noticed that it wasn’t just Backup that was the problem it was all network IO through a local vswitch. He started the conversation by asking me what I expect to see in network throughput between 2 VMs localised on the same vswitch. He informed me no matter what he tried in terms of using a vswitch with/without a pNIC and trying different types of vNIC he couldn’t push 240mbits/s. He asked him the obvious question which was “Is there anything else happening on the system that could be impacting net performance, like CPU overhead” and the answer was “no”.
So I decided to test it for myself.

As did my client I used the Netperf tool to test throughput between the 2 VMs. To use NetPerf you run:
C:\Netserver.exe on one VM
and then 
C:\Netclient.exe –H hostname (of the first system)
on the other VM.

After a few seconds you should get a result displayed in mbits/s
And just like my client I tested a vswitch with/without a pNIC and different types of vNIC. I also tested different hosts to get varied result. The problem is I saw results which I’d expect to see, and on average I saw speeds of 500mbits/s

Flexible 1 2 Average
vswitch +pNIC 502 594 548
vswitch -pNIC 608 565 586.5
vswitch +pNIC 461 482 471.5
vswitch -pNIC 261 495 378
VMXNet3 1 2 Average
vswitch +pNIC 641 621 631
vswitch -pNIC 628 593 610.5
vswitch +pNIC 465 496 480.5
vswitch -pNIC 531 533 532

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