HA works differently on a VSAN cluster than on a non-VSAN cluster.
- When HA is turned on in the cluster, FDM agent (HA) traffic uses the VSAN network and not the Management Network. However, when a potential isolation is detected HA will ping the default gateway (or specified isolation address) using the Management Network.
- When enabling VSAN ensure vSphere HA is disabled. You cannot enable VSAN when HA is already configured. Either configure VSAN during the creation of the cluster or disable vSphere HA temporarily when configuring VSAN.
- When there are only VSAN datastores available within a cluster then Datastore Heartbeating is disabled. HA will never use a VSAN datastore for heartbeating as the VSAN network is already used for network heartbeating using the Datastore for heartbeating would not add anything,
- When changes are made to the VSAN network it is required to re-configure vSphere HA.
ESXi Isolation – VM with no underlying storage
- HA will detect there are no network heartbeats received from ESXi Host 4
- HA master will try to ping ESXi Host 4
- HA will declare ESXi Host 4 as unavailable
- VM will be restarted on one of the other hosts
When there is no resilient storage solution (outwith VSAN) it is important to ensure that isolation response is set to power-off.
ESXi Isolation – VM with underlying storage
In this example we will discuss what would happen if ESXi Host 1 and 4 were both in the same partition.
This scenario is slightly more complex. There are two partitions, one of the partition is running the VM with its VMDK and the other partition has a VMDK and the witness. In this scenario VSAN uses the witness to see which partition has. In this case the partition that has more than 50% of the VSAN is the winner. This means that the VM will be restarted on either ESXi Host 2 or 3 by HA.
ESXi Isolation – VM with Witness
In this case the partition that has more than 50% of the VSAN is the winner. This means that the VM will be restarted on either ESXi Host 1 or 2 by HA.