You can use vSAN as the shared storage for a vSphere HA cluster. If enabled, vSAN aggregates the specified local storage disks available on the hosts into a single datastore shared by all hosts.
To use vSphere HA with vSAN, you must be aware of certain considerations and limitations for the interoperability of these two features.
ESXi Host Requirements
You can use vSAN with a vSphere HA cluster only if the following conditions are met:
- All the cluster's ESXi hosts must be version 5.5 or later.
- The cluster must have a minimum of three ESXi hosts.
vSAN has its own network. If vSAN and vSphere HA are enabled for the same cluster, the HA interagent traffic flows over this storage network rather than the management network. vSphere HA uses the management network only if vSAN is disabled. vCenter Server chooses the appropriate network if vSphere HA is configured on a host.
If you change the vSAN network configuration, the vSphere HA agents do not automatically pick up the new network settings. To make changes to the vSAN network, you must take the following steps in the vSphere Client:
- Disable Host Monitoring for the vSphere HA cluster.
- Make the vSAN network changes.
- Right-click all hosts in the cluster and select Reconfigure for vSphere HA.
- Re-enable Host Monitoring for the vSphere HA cluster.
vSphere HA Networking Differences shows the differences in vSphere HA networking whether or not vSAN is used.
|vSAN Enabled||vSAN Disabled|
|Network used by vSphere HA||vSAN storage network||Management network|
|Heartbeat datastores||Any datastore mounted to > 1 host, but not vSAN datastores||Any datastore mounted to > 1 host|
|Host declared isolated||Isolation addresses not pingable and vSAN storage network inaccessible||Isolation addresses not pingable and management network inaccessible|
Capacity Reservation Settings
When you reserve capacity for your vSphere HA cluster with an admission control policy, you must coordinate this setting with the corresponding vSAN setting that ensures data accessibility on failures. Specifically, the Number of Failures Tolerated setting in the vSAN rule set must not be lower than the capacity that the vSphere HA admission control setting reserved.
For example, if the vSAN rule set allows for only two failures, the vSphere HA admission control policy must reserve capacity that is equivalent to only one or two host failures. If you are using the Percentage of Cluster Resources Reserved policy for a cluster that has eight hosts, you must not reserve more than 25% of the cluster resources. In the same cluster, with the Host Failures Cluster Tolerates policy, the setting must not be higher than two hosts. If vSphere HA reserves less capacity, failover activity might be unpredictable. Reserving too much capacity overly constrains the powering on of virtual machines and intercluster vSphere vMotion migrations.