HP Serviceguard manual To Arbitrate or Not to Arbitrate, No Arbitration-Multiple Paths

Arbitration for Data Integrity in Serviceguard Clusters

To Arbitrate or Not to Arbitrate

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

8