what is fortigate HA heartbeat traffic bandwidth is

Hi,

I have something unclear about statement below when enable set session-sync-dev portx portx

Moving session synchronization from the HA heartbeat interface reduces the bandwidth required for HA heartbeat traffic and may improve the efficiency and performance of the cluster.

 So, what is the HA heartbeat interface bandwidth required or what bandwidth will be if configure the interface to be heartbeat link? I thought HA heartbeat interface bandwidth should be like other interface 1G port or more than it (SFP is 10G). Thus i have no idea any benefit to set session-sync-dev portx portx, if HA heartbeat interface bandwidth is same as other interface.

anyone can help to advise?

Thanks.