To survive a failure of the Edge without downtime, you must deploy a second appliance. If you configure two appliances as an HA pair, the Edge can continue serving exports without disruption to the servers in the branch, even if one of the Edge appliances were to fail.

The scenario described in this section has two Edges operating in an active-standby role. This scenario is irrespective of whether the Core is configured for HA in the data center.

The active Edge is connected to the Core in the data center and is responding to the read and write requests for the exports it is serving in the branch. This method of operation is effectively the same as with a single Edge; however, there are some additional pieces that make up a complete HA deployment.

The standby Edge does not service any of the read and write requests but is ready to take over from the active peer.

As the server writes new data to exports through the blockstore of the active Edge, the data is reflected synchronously to the standby peer blockstore. When the standby peer has acknowledged to the active peer that it has written the data to its own blockstore, the active peer then acknowledges the server. In this way, the blockstores of the two Edges are kept in lock step.

Prior to release 4.2, although two interfaces are configured, only one interface is actively sending blockstore synchronization traffic. The Edge software includes Multipath NetDisk. With this new feature, you can load balance the blockstore synchronization traffic across both interfaces. Multipath NetDisk continues to provide resiliency for the blockstore synchronization but also delivers higher performance. You do not need to do any additional configuration to enable this capability if both Edges are running release 4.2.

If the interfaces used for blockstore synchronization are of different capacities (for example, one is 1 Gbps and the other is 10 Gbps), then we recommend that you specify the higher capacity interface first.