2.2.4 vSAN and vSphere HA considerations
The combination of vSAN as a highly available storage infrastructure and vSphere HA as a highly available solution for virtual machine compute resources provides a powerful synergy for delicate workloads.
The following are requirements for the interoperability of vSAN and vSphere HA to function:
• vSAN must be configured on the cluster before enabling vSphere HA, or vSphere HA must be temporarily disabled to allow vSAN configuration
• vSphere HA must use the vSAN network for its communication
• vSphere HA must not use the vSAN datastore as the Heartbeat datastore
• vSAN and vSphere HA do not interoperate to pre-allocate storage resources in case of a host failure, contrary to what vSphere HA does by reserving CPU and memory resources. The storage sizing is a task delegated to the administrators.
The following figure illustrates the dynamic of the vSphere HA feature in action at the occurrence of a failure of a single host within the pool of nodes in a cluster. When the failure occurs, the computing resources and the portion of the datastore storage allocated from the lost node become unavailable. vSphere HA then restarts the virtual machines previously running on the failed node, redistributing them across the remaining nodes of the cluster.
Figure 4. vSphere High Availability in Action
