A pair of Cores deployed in an HA-failover cluster configuration are active-active. Each Core is the primary to itself and secondary to its peer. Both peers in the cluster are attached to storage in the data center. But individually they each are responsible for projecting one or more exports to one or more Edge appliances in branch locations.

Each Core is configured separately for the exports and the Edges it is responsible for. By default in a Core HA deployment, storage is automatically configured for failover.

As part of the HA deployment, you configure each Core with the details of its failover peer. This deployment comprises two IP addresses of network interfaces called failover interfaces. These interfaces are used for heartbeat and synchronization of the peer configuration. After the failover interfaces are configured, the failover peers use their heartbeat connections (failover interfaces) to share the details of their storage configuration. This information includes the exports they are responsible for and the Edges they are projecting the exports to.

If either peer fails, the surviving Core can take over control of the exports from the failed peer and continue projecting them to the Edges. During a failover scenario, all projected exports are set to read-only by the Core. The Edges will absorb writes locally in the blockstore and acknowledge, but commits will be paused until the failed Core recovers.

Core HA failover is triggered at the Core level. If an Edge loses connection to its primary Core, but still has connectivity to the secondary Core, no failover occurs. No failover occurs because both Cores continue to detect each other's heartbeat through the failover interfaces. The Edge enters a disconnected operations state as normal and saves write operations to the blockstore until connectivity to the primary Core is restored.

Make sure that you size both failover peers correctly so that they have enough capacity to support the other Core storage in the event of a peer failure. If the surviving peer does not have enough resources (CPU and memory), then performance might degrade in a failure situation.

After a failed Core has recovered, the failback is automatic.