HW Failover - what's behind it?

Not sure if this helps. Also, I'm sure if you use Network & Serial failover, both must fail in order for a failover to occur but that may have changed;

 

 

"Serial Failover is used to failover between two devices in an active/standby HA Pair or DSC Device Group with only two members; it cannot be used with VIPRION or an active/active HA Pair. It is the recommended failover method due to its speed; failing over in under 1s when a relevant event occurs and causes the loss of the ‘heartbeat’ on the cable. Except in the case of a power failure on the primary unit, failover will not actually occur between devices unless additional HA features such as Fail-safe or a HA Group are configured to trigger it.

 

 

The maximum serial cable length is 50 feet; devices any further apart must use Network Failover.

 

 

Where possible, Connection, Persistence and SNAT mirroring should be used to minimise the effects of failover and failback on client connections and traffic flow."