Arbitration For Data Integrity in Serviceguard Clusters, July 2007

Arbitration for Data Integrity in Serviceguard Clusters
To Arbitrate or Not to Arbitrate
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To Arbitrate or Not to Arbitrate
Arbitration is not always used to determine cluster membership. Some
cluster software products rely exclusively on the use of multiple cluster
membership communication links (heartbeats). These algorithms are
described in the following sections.
No Arbitration—Multiple Paths
Some approaches do not use arbitration, but instead rely on multiple
membership paths to ensure that the heartbeat or essential intra-cluster
communication remains unbroken. In this approach, the event of a node
failing entirely is considered more likely than the event of several LAN
paths all failing at the same time. Such systems assume that a loss of
communication means a node failure, and packages are allowed to fail
over when a loss of heartbeat is detected.
This model is illustrated in Figure 1 and Figure 2. In Figure 1, three
separate LAN failures would be required to break communication
between the cluster nodes. This assumes that hubs are separately
powered, of course, and that other HA design criteria are met.
Figure 1 Multiple Heartbeat Failures