Vsan Witness Virtual Appliance

VSAN 6.1 has been released for two or three months, with 2 notable new features, one of which is support for stretched Cluster, which means that your Vsan cluster can now be located in a physical location, deployed across data centers, and a 2-node Vsan.

We know that the original Vsan needs at least 3 nodes, why? Since the default FTT is 1, each data disk requires at least 3 components, 1 copies of data, 1 copies of the data, the 3rd is the witness component (Witness component), the equivalent of the quorum disk in the cluster, to solve the problem of brain crack. In other words, "If you want to make the disk object of a virtual machine usable, it must have more than 50% components available, and the witness is used to solve the problem of more than 50%."

Originally Witness is a component exists in a Vsan cluster on a physical host, and now, Witness appliance can exist as a virtual machine, it exists to store Witness component. In this way, the minimum limit on the number of physical hosts for a Vsan cluster is reduced by one.

Remember:

Witness appliance is used to replace an ESXi host.

Witness appliance is used to replace an ESXi host.

Witness appliance is used to replace an ESXi host.

The important thing to say three times. So deploy it as an ESXi host to deploy it.

So, of course, you can also deploy a physical machine to do the same thing. But the point here is that we want to save money and save a host, don't we? Then, in order to save money with a special virtual machine to replace the physical host, you have to consider this special virtual machine more.

Configuration Requirements for Witness appliance

Witness Appliance is a virtual machine, how should the hardware of this virtual machine be configured? Vsan clusters of different sizes have different requirements for the configuration of Witness appliance:

Micro-environment (less than 10 virtual machines)

• 2 Vcpus, 8GB VRAM

• 8GB ESXi Boot Disk, one 10GB SSD, one 15GB HDD

• Supports a maximum of 750 witness component

Medium environment (up to 500 virtual machines)

• 2 Vcpus, 16GB VRAM

• 8GB ESXi Boot Disk, a 10GB SSD, a 350GB HDD

• Supports a maximum of 21,000 witness component

Large environments (more than 500 virtual machines)

• 2 Vcpus, 32GB VRAM

• 8GB ESXi Boot Disk, 10GB SSD, three 350GB HDD

• Supports a maximum of 45,000 witness component

Note that the so-called SSD is not a real SSD, but an SSD-tagged vmdk.

Network Requirements for Witness appliance

Another very important one is the network configuration of the witness appliance. Because the network is not able to do arbitration ah. (This is not nonsense, laugh)

Therefore, the network card of this virtual machine must be able to communicate with other hosts in the Vsan cluster. And DNS is important, but also to add domain. It also needs to be joined to Vcenter as an ESXi host.

Since witness appliance is treated as an ESXi host, it will have its own vswitch. The MAC address of the uplink network port of the standard vswitch in witness appliance should be set manually as the MAC address of the host on which it resides. Thus, the witness request submitted to the host can be passed on to the witness appliance.

Note that the Witness appliance is currently designed for the 2 node Vsan cluster. Regular 3-node (or more-node) Vsan clusters still use traditional methods, witness component or scattered across all hosts in the cluster.

Application Scenarios

The problem comes, Witness appliance is also on a host, and this host can not be a 2-node Vsan in a cluster of one, that is not to say or need 3 host? Since there are 3 hosts, then why bother to specialize, directly build a regular 3-node Vsan cluster can not?

Well, that's a good question to ask, but the 2-node Vsan scenario is not the same, it's mostly used for robo scenarios. Robo is remote Office/branch office, a small branch office where 2 hosts can meet demand for smaller offices, and 3 hosts can be a bit wasteful. In this scenario, the Witness appliance is installed on an ESXi host on the head Office's data center.

Extremely important reference documents:

http://cormachogan.com/2015/03/13/vsan-6-0-part-1-new-quorum-mechanism/

http://cormachogan.com/2015/09/11/a-closer-look-at-the-vsan-witness-appliance/

For a testimonial, please refer to the http://vsdsrevolution.blog.51cto.com/8674155/1423897

My article basically is to refer to the article of Cormac, and express it in the way of own understanding. Swim, on paper, laughed at. English good students or recommend directly to read the original.

This article from the "Triangle Balcony Technical Notebook" blog, reproduced please contact the author!

Vsan Witness Virtual Appliance