Quick tip on circumventing a known limitation of HCI solutions with NFS v4 datastores and vCHA.
vCenter Server Appliance (vCSA) in High Availability mode is made up of 3 instances – Active, Passive and Witness nodes.
At least 2 of the 3 instances (active, passive or witness) must be running all the time for vCenter Server HA to work.
To achieve true HA of the vCenter Server, it is recommend to place at least the witness instance on a separate ESXi Host or Cluster than the active and passive instances. This is due to the fact that – consider there are 2 clusters, 3 instances will most probably be split as 1 of 3 in 1st cluster and remaining 2 of 3 in the 2nd cluster. Now if the 2nd cluster goes bad, there will be no vCenter Server access, let alone the HA!
Ideally, all the 3 instances should be in 3 different clusters.
In smaller environments with 1 or 2 clusters, you may need to place 2 or all of the 3 instances in the same cluster. In such scenarios, you might encounter errors at the cloning stage (Active instance is deployed first and then it is used as a base template for cloning Passive and Witness with appropriate network settings [2 and 1 vNIC/adapter] – all of this is done by the vCHA automation process or could be done manually as well by creating a Guest OS customization specification). This is due to a known issue related to NFS v3 datastore (Ref).
Solution is to use a NFS v4 datastore or to place the Witness instance on a different datastore than the Active instance. Pick the latter in case of HCI solutions which are only to able to create NFS v3 datastores.
This has been tested with Cisco HyperFlex (Ref). But same is the case with others HCI OEM vendors.
IT Findings 