speed in an internal vswitch

[nik-O]

Hello,

if 2 virtual machines are connected to the same virtual switch (meaning the packets transferred don't go through the physical adapter), what is the maximum actual possible speed? (with vmxnet driver) is it limited by the driver itself, by the ip vmkernel stack or what ?

thank you by advanced.

Nico

[SuryaVMware]

VMKernel ip stack has no role to play here. The speed between the VMs will only be limited by the way vNIC is implemented and the driver in the respective GOS.

Hope this answers your question.

-Surya

[SuryaVMware]

If you decided to do some test, the following links should help you in what to look for and what to test.

http://www.vmware.com/files/pdf/ESX_networking_performance.pdf

http://www.vmware.com/files/pdf/perf_comparison_virtual_network_devices_wp.pdf

-Surya

[atbnet]

The virtual NICs will show as 1GB, you could also add up to 4 and team them in the OS. However this is also finally restricted by the CPU an IO throughput of the server, which can vary of course.

Andy, VMware Certified Professional / VMware vExpert Award 2009

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[RParker]

what is the maximum actual possible speed?

I don't think anyone actually READ the question.

1Gig is the answer (120 MB/s).

[mcowger]

FALSE.

The max speed is the internal speed if the vSwitch, which can EASILY exceed 1Gbit. More like multi gigabit.

--Matt

VCP, vExpert, Unix Geek

[dilidolo]

This is the test I did in my test lab

# iperf -c debian5 -w 64K

-

---

Client connecting to debian5, TCP port 5001

TCP window size: 128 KByte (WARNING: requested 64.0 KByte)

-

---

local 192.168.111.10 port 35708 connected with 192.168.111.135 port 5001

Interval Transfer Bandwidth

0.0-10.0 sec 4.23 GBytes 3.63 Gbits/sec

[SuryaVMware]

Speed settings that are shown are only the representations of the NIC implemented.

PCNET32 will show 10mbps, that dosen't mean the VM will not get more than 10 mbps, Depends on where the communication is, it can get as much as the underlying physical NIC can allow at that point in time.

If the Communication is with in the vSwitch, then the packets are not even going through the pNIC. In this case the system I/O bus and the way the vNIC is implemented will the limitation along with how well the driver is written.

Now you may ask why do we have so many vNICs implemented if the speed is not limited to what is shown on the vNIC. Not all vNIC implementations are the same for example the Enhanced VMXNET implementation supports Jumbo frames.

-Surya

[RParker]

The max speed is the internal speed if the vSwitch, which can EASILY exceed 1Gbit. More like multi gigabit.

You have a document to back that up? Show me the technical specs on the vSwitch architecture that says that it can go over 1Gb of SPEED, not bandwidth.

They aren't the same thing. I can have a 1/2 garden hose that I can have water coming out to fill up a gallon bucket in say 30 seconds. I can take a 6' pipe but no more water coming out than before, more bandwidth but necessarily more flow speed.. It still takes the same time to fill up the bucket.

So you produce the documents that prove your point, then I will believe you.

[RParker]

This is the test I did in my test lab

Is this test data a 64k file? That's rather small if it is.. If it's a bigger file, then add more nics to the VM, and do the same transfer, more bandwidth means more transfer rate if these numbers are correct.

so if you stream a 10G file let's say, and it takes 1 min, if you had another nic you should be able to send that file in 30 seconds... But I think you will find this doesn't occur, even on an internal switch.

[nik-O]

So .... what'is the maximum speed ? xD ... from a theory point of view?

[mcowger · Accepted solution]

I do - see dilidolo's tests below - I have the same results.

that '64k' is a TCP window size, not a file size. The data data xfered was 4.23GBytes in 10 seconds. Who needs a document when you have test results If you really want a document, check out page 4 of 'Virtual Networking Concepts PDF:

"Note: The speed and duplex settings found in physical networking are not relevant in the virtual network, because

all the data transfer takes place in the host system’s RAM"

As far as theoretical speed limit - I'm not sure there is one - I'm sure its limited by your hardware.

--Matt

VCP, vExpert, Unix Geek