Chapter 15 Unified Threat Management for FortiOS 5.0 : Intrusion protection : IPS processing in an HA cluster : Active-active
  
Active-active
The fail-over process in an active-active cluster is similar to an active-passive cluster. When the primary unit fails, a secondary unit takes over and traffic processing continues. The load-balancing schedule used to distribute sessions to the cluster members is used by the new primary unit to redistribute sessions among the remaining subordinate units. If session pick-up is not enabled, the sessions active on the failed primary are lost, and the sessions redistributed among the secondary units may also be lost. If session pick-up is enabled, all sessions are handled according to their last-known state.
For more information about HA options and settings, see “High Availability for FortiOS 5.0”.