You can use Virtual SAN as the shared storage for a vSphere HA cluster. When enabled, Virtual SAN aggregates the specified local storage disks available on the hosts into a single datastore shared by all hosts.

To use vSphere HA with Virtual SAN, you must be aware of certain considerations and limitations for the interoperability of these two features.

For information about Virtual SAN, see vSphere Storage.

ESXi Host Requirements

You can use Virtual SAN with a vSphere HA cluster only if the following conditions are met:

  • The cluster's ESXi hosts all must be version 5.5 or later.

  • The cluster must have a minimum of three ESXi hosts.

Networking Differences

Virtual SAN has its own network. When Virtual SAN and vSphere HA are enabled for the same cluster, the HA interagent traffic flows over this storage network rather than the management network. The management network is used by vSphere HA only when Virtual SAN is disabled. vCenter Server chooses the appropriate network when vSphere HA is configured on a host.

Note:

Virtual SAN can only be enabled when vSphere HA is disabled.

If you change the Virtual SAN network configuration, the vSphere HA agents do not automatically pick up the new network settings. So to make changes to the Virtual SAN network, you must take the following steps in the vSphere Web Client:

  1. Disable Host Monitoring for the vSphere HA cluster.

  2. Make the Virtual SAN network changes.

  3. Right-click all hosts in the cluster and select Reconfigure HA.

  4. Re-enable Host Monitoring for the vSphere HA cluster.

The following table shows the differences in vSphere HA networking when Virtual SAN is used or not.

Table 1. vSphere HA networking differences

Virtual SAN Enabled

Virtual SAN Disabled

Network used by vSphere HA

Virtual SAN storage network

Management network

Heartbeat datastores

Any datastore mounted to > 1 host, but not Virtual SAN datastores

Any datastore mounted to > 1 host

Host declared isolated

Isolation addresses not pingable and Virtual SAN 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, this setting must be coordinated with the corresponding Virtual SAN setting that ensures data accessibility on failures. Specifically, the Number of Failures Tolerated setting in the Virtual SAN rule set must not be lower than the capacity reserved by the vSphere HA admission control setting.

For example, if the Virtual SAN 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 less capacity is reserved by vSphere HA, failover activity might be unpredictable, while reserving too much capacity overly constrains the powering on of virtual machines and inter-cluster vMotion migrations.