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VM machines communication

Posted on 2014-03-17
Last Modified: 2014-04-01
In most environments , VMs are store in a SAN.
so in Vsphere client if we go to Networking, we'll see a virtual switch with 1 or more physical NICs and VM port group, the physical NICs of the Virtual Switch , if I understand are the ones plugged to ESX host…correct?

so if VM1 wants to talk to VM2 , while both are in the SAN, would VM1 will go out of the SAN NIC then through physical NIC on ESX host then come back through that physical NIC to the SAN NIC  in order to talk to VM2 which is in fact in the same SAN as VM1 ?

Any explanation will be very much appreciated.

Thank you.
Question by:jskfan
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LVL 119
ID: 39935740
The physical network interfaces in the host ESXi server physical uplinks are connected to a vSwitch.
So you are correct with your logic.

Its got nothing to do with SAN.

Network traffic leaves the VM via its network interface connected to a virtual machine port group.

The virtual machine port group is connected to a vSwitch.

If both VM1 and VM2 are connected to vSwitch traffic will pass between the VMs.

The host server controls communication to your SAN in the background via whatever topology that us...FC iSCSI or NFS
LVL 55

Expert Comment

ID: 39936518
The VMs reside on the SAN but they run on the host. Just like a PC the OS resides on a hard disk but it runs on the CPU/RAM. If you transfer a file from one VM to another then it does go SAN-VM-VM-SAN so does go over the SAN twice.

Author Comment

ID: 39937785
VM1 and VM2 physical files are in the SAN , physical NIC that Virtual switch is connected to is on the ESX Host…so if VM1 wants to Talk to VM2 , what would be the route it will take ?
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LVL 55

Accepted Solution

andyalder earned 250 total points
ID: 39937859
Straight through the virtual switch on the host, no external network traffic would exist if it was a simple ping or remote control session. There could be some traffic on the SAN though since ping.exe would have to be transferred from the disk to RAM over the SAN before it could be executed.
LVL 119
ID: 39938064
The vSwitch the virtual machine port groups are connected to.

Author Comment

ID: 39947458

I agree, the VM Operating System is in the SAN.
RAM/CPU and Network Adapter are on the ESX Host.

if the SAN is 30 feet away from ESX Host, then there should be some communication that goes between the VM OS located in the SAN and its Resources that are on ESX host..

 I Want to understand the communication road map…what are the entrance/exit points that the communication will take.
LVL 55

Expert Comment

ID: 39947655
The VM doesn't run on the SAN, it is stored there. The communication between RAM and disk is exactly the same in a physical environment as in a virtual one except that in this case your VM's disk is separated from the host by Ethernet rather than SCSI cable.

Author Comment

ID: 39953348
So there are still those trips between the VM OS in the SAN and RAM/CPU/NIC  which in ESX host.

for instance: let's say I have a script that runs on VM1 that copies files to VM2… (VM1 and VM2 are in the SAN)
I believes those files will not end up on VM2, without involving RAM/CPU/NIC adapters that are in ESX
LVL 119

Assisted Solution

by:Andrew Hancock (VMware vExpert / EE MVE^2)
Andrew Hancock (VMware vExpert / EE MVE^2) earned 250 total points
ID: 39953473
That assumption is correct.
LVL 55

Expert Comment

ID: 39953834
The file transfer I described a week ago - SAN to VM (on host), then VM to VM (on same host so no LAN traffic), then VM on host to SAN. The only way to avoid the file traversing the SAN twice is to use a shared filesystem such as StorNext and its client installed on each VM which is prohibitively expensive.

Author Closing Comment

ID: 39968678
Thank you Guys!

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