Arbitration For Data Integrity in Serviceguard Clusters, July 2007

Arbitration for Data Integrity in Serviceguard Clusters
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Arbitration for Data Integrity in
Serviceguard Clusters
Clustering is an architecture of interconnected servers that allows
multiple hosts to run the same applications, permitting the individual
systems to be up or down. Applications move easily between systems,
accessing the same shared data from different nodes at different times.
The goal is to provide high availability for the application and the data
without endangering the integrity of the data. Particularly, the cluster
manager software must ensure that when an application is running and
processing data on one node in the cluster, the same application does not
inappropriately start up on another node and begin processing the same
data at the same time. Cluster software must protect data integrity at all
costs.
Different clustering solutions have adopted various methods for ensuring
the safety of data. Some solutions rely solely on redundant membership
links to ensure data integrity. Others, including the Serviceguard
product family, use a process called arbitration to keep more than one
incarnation of a cluster from running and starting up a new instance of
an application. The Serviceguard team has always agreed that definitive
arbitration should be used in high availability systems that run
mission-critical applications.
This paper describes some basic cluster membership concepts, then
discusses some different ways of determining cluster membership.
Several types of arbitration are shown with example configurations that
illustrate each type. Then the arbitration methods used by Serviceguard
and related products are presented in some detail.
NOTE Some of the arbitration methods mentioned in this paper are available
only on particular platforms or with specific types of configuration. Other
methods, while possible, have not been fully tested on all types of
systems. For details about support of particular kinds of arbitration,
refer to your platform’s Configuration Guide, available through your HP
representative.