Why vSphere Distributed Switch on vSAN?

For those who are not aware, vSphere Distributed Switch (or abbreviated as vDS) is included as part of the vSphere Enterprise Plus edition license.

 

What exactly is a vDS?

In some sense, the vSphere Distributed Switch is pretty similar to a vSphere Standard Switch (vSS). It provides the connectivity between your virtual machines and the outside world. The main difference is that vDS is meant to provide you with a consistent switch configuration across all the hosts in your datacenter.

 

vDS

vSphere Distributed Switch Architecture | Source

vSphere Distributed Switch is pretty useful in some sense. It provides a centralized management for all your virtual machine networking where you can configure and monitor the configurations from a single source. If you vMotion a VM from one host to another, the VM will and can maintain its networking settings.

vDS allows different hosts to be connected to this single switch as long as they are within the same host cluster. This is significantly different from the familiar vSphere Standard Switch (vSS) that we know of, where you have to configure one vSS per ESXi host.

vSS

vSphere Standard Switch Architecture | Source

vSphere Standard Switch may be sufficient for environments where there are very few ESXi hosts to manage. However, if your environment is pretty sizeable, it will be painful to manage all your vSS (since you need one per ESXi host).

Another point to note is that since vSS is configured and stored on each ESXi host, if the configuration screws up somehow, you will need to reconfigure it from scratch. For vDS, it is deployed from vCenter. As long as you have vCenter up and running, you should be safe.

Of course with that being said, if vCenter ever fails, do take note that the VMs using a vSphere Distributed Switch will continue to run as per normal even if vCenter is unavailable. You will not be able to configure the switch or add VMs to the switch, but it will run fine!

 

PSA: vDS comes free in ALL vSAN editions!

What a lot of people may not know is that vDS is also included for free in ALL editions of vSAN. Why is this so?

Aside from all the obvious benefits that comes with centralised management of switches, there is also an additional benefit as to why you should be using vDS in your vSAN environment.

 

What is it?

Network I/O Controls.
Note: Network I/O Control is a feature that is only available when you have vDS. 

What Network I/O controls does is it allows you to reserve or allocate bandwidth to business-critical applications based on the concepts of Shares, Reservations and Limits. This is extremely useful in situations such as contention whereby different types if applications are competing against each other for a pool of common resources.

Think of it this way- all your business-critical applications want to run at its optimum, but it is not able to do so because it is not able to get all the resources it needs in order to do so.

So what Network I/O Control does is that it ensures that the different types of traffic are able to get the network bandwidth it requires.

 

So how is this related to vSAN?

With Network I/O Control, VMware provides a way for you to implement Quality of Service (QoS) on network traffic. Since vSAN traffic does not have its own dedicated network interface card (NIC) and has to share the physical NIC with other types of traffic such as Virtual Machine Traffic, Management Traffic and vMotion traffic…etc., this could be very useful.

But of course, do take note that there are several recommendations that VMware gives with regards to setting Shares, Limitations or Reservations.

For more information on what VMware’s recommendations are, please feel free to browse this link.

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