Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : HA heartbeat and communication between cluster units : Modifying heartbeat timing : Changing the lost heartbeat threshold
  
Changing the lost heartbeat threshold
The lost heartbeat threshold is the number of consecutive heartbeat packets that are not received from another cluster unit before assuming that the cluster unit has failed. The default value is 6, meaning that if the 6 heartbeat packets are not received from a cluster unit then that cluster unit is considered to have failed. The range is 1 to 60 packets.
If the primary unit does not receive a heartbeat packet from a subordinate unit before the heartbeat threshold expires, the primary unit assumes that the subordinate unit has failed.
If a subordinate unit does not receive a heartbeat packet from the primary unit before the heartbeat threshold expires, the subordinate unit assumes that the primary unit has failed. The subordinate unit then begins negotiating to become the new primary unit.
The lower the hb-lost-threshold the faster a cluster responds when a unit fails. However, sometimes heartbeat packets may not be sent because a cluster unit is very busy. This can lead to a false positive failure detection. To reduce these false positives you can increase the hb-lost-threshold.
Use the following CLI command to increase the lost heartbeat threshold to 12:
config system ha
set hb-lost-threshold 12
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