Number of NICs in VM ?

[hoff316]

I am setting up a ESX server and my server has four 1000 mbs NICs. I created a VM with Windows2003 server and turned on all four NICs in the VM assigning a unqiue ip to each. Before I get too far into my configuration, does this help my performance or should I just configure one or two Network interface cards in the VM ? I plan to run a number of VM's on this server and I was wondering if I am creating a potential performance problem by turning all NICs on in the VMs. Thanks for any comments and suggestions.

[kharbin]

You only need supply a VM with (1) vNIC unless you need access to multiple networks. All NIC bonding is done at the ESX level, not inside th guest. You need to create a vSwitch and assign the (4) physical nics to it. then attach the vNIC of the VM, to the vSwitch.

The ESX Admin Guide describes this feature in detail.

[Mike_Fink]

VMware does not do a typical NIC "bond" that you may be used to if you deal with other operating systems on a regular basis.

For example, if you make a VSwitch with 4 1GB NICs, and you connect one VM to this switch, how much bandwidth is available to this VM? 1GB/s. The VSwitch in VMware is really a switch, it functions just like a typical switch in your infrastructure. Think of it as a single switch with 4 1GB uplinks back to your core switch; that's really what you have. The only way to EVER get 4GB/s moving through the VSwitch is to have 4 VMs all powered on, and all sending or recieving 1GB/s. There is no possible way that a single VM can consume more then 1GB/s, as it only has one connection into the VSwitch.

In a typical configuration, you will assign one NIC per VM, and then assign as many PNIC (physical NICS) as needed to the VSwitch. 4 is plenty. You should divide those 4 physical connections over 2 switches (no special configuration is needed, I can explain why if your interested, but just know that for typical VMWare NIC balancing there is nothing needed on most switches). If one switch fails, all the VMs that were using the 2 physical connections will immediately ARP their MAC addresses down the remaining 2 paths to the other (still active) switch.

If you really need to get more then 1GB/s into the VM (which, I would point out, is VERY, VERY rare) you will need to create 2 NICs inside the VM, and then present 2 IP addresses out of the host (or use some load balancing software inside the VM). This is an unusual configuration; I have needed to do it several times, but never for bandwidth reasons. 1GB/s is more then enough for almost anything you should ever run inside of VMware!

Hope this helps.