What is the witness node really used for and what hardware does everyone buy to run this?

[mmaus]

I have been able to get HA to failover between just two host...the primary and the backup with no witness node installed or configured. 

Sooooo...why does VMware say we need a witness node?  What else is it being used for? and what hardware does everyone seem to use for this witness node as it almost seems like just a monitoring station that I am guessing requires another VMware license to really not do much of anything...?

Im not trying to be cocky or anything...really trying to understand and justify the cost of a third piece of hardware with matching license.

[daphnissov]

With vSphere HA there is no such concept of a witness node. With vCenter HA (vCHA), there is. The two are totally different technologies and you're probably confusing one with the other.

[mmaus]

I did intent to say vCenter...not vSphere.

My vBrain is going into vOverload trying to solve my vBudget limit vs my vClientRequest

v v v v v v v v v v v

[daphnissov]

Ok. If you only have a 2-node cluster like you mentioned in your thread here, having vCenter HA is really not going to help you as any single host failure will take out two of the three nodes rendering vCenter unavailable. The witness node is a virtual appliance just like vCSA and runs on an ESXi host.

[mmaus]

I guess this is where my confusion resides....

I have Host A, and Host B.

Host A is running VMs,

Host B is running vCenter.

If I kill the power to Host A...all the VMs migrate over to Host B....I then can restore power to Host A and re-establish the cluster...

I can then kill the power on Host B and have all VMs and vCenter migrate over to Host A...  it takes a 10-15min before vCenter has initialized and is ready to be logged in again, but it does seem to work with no witness node.

If the Witness node is a virtual appliance...does it run on both physical host?

[daphnissov · Accepted solution]

What you're describing is vSphere HA and not vCenter HA. The concept requiring a witness is vCenter HA which works differently by protecting vCenter directly from things such as logical corruption and not merely ESXi host failures. As I said, if you only have a 2-node cluster, then don't even look at vCHA as it's a waste of effort. With 2 nodes, you don't have enough cluster resources to run vCHA correctly.

[mmaus]

I think I see what you are saying.  Thank you for the input.  I think I see the knowledge path I need to go down now.