If the heartbeat is lost for a particular node, the clustering software will
interrogate the quorum to determine which surviving node should take ownership of
resources from the lost node.
Therein lies the rub with the heartbeat mechanism: any network disruption with the
heartbeat communication can initiate some sort of failover. Three to five years ago, this
was a real concern. Today, networks (and those that manage them) have come a long way.
It??™s less likely that network failure will be a problem unless there is a hardware issue with
the network card. Still, it can occur, particularly in a poorly configured environment.
Network cards and routers run at different speeds (such as 10Mbps, 100Mbps, and
1000Mbps) and in different modes (half duplex and full duplex). If the network cards and
any other network devices aren??™t configured to dynamically establish the proper speed
and mode for optimal communication, heartbeat interruptions can occur. This can happen
with cheap equipment or with quality equipment that has a slight defect.
A heartbeat interruption can be extremely difficult to diagnose, often causing DBAs
to hard-code speed and duplex mode settings or temporarily remove a node from a cluster.
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