Arbitration For Data Integrity in Serviceguard Clusters, July 2007

Arbitration for Data Integrity in Serviceguard Clusters
Cluster Membership Concepts
7
Tie-Breaking
Tie-breaking (arbitration) is only required when a failure could result in
two equal-sized subsets of cluster nodes each trying to re-form the
cluster at the same time. These competitors are essentially tied in the
contest for the cluster’s identity. The tie-breaker selects a winner, and
the other nodes leave the cluster.
Tie-breaking is done using several techniques in Serviceguard clusters:
• Through a cluster lock disk, which must be accessed during the
arbitration process. This can be used with clusters of up to 4 nodes in
size. This type of arbitration is available only on HP-UX systems.
• Through a cluster lock LUN, a variant of the lock disk, for clusters of
up to 4 nodes.
• Through arbitrator nodes, which provide tie-breaking when an entire
site fails, as in a disaster scenario. Arbitrator nodes are cluster
members located in a separate data center whose main function is to
increase the cluster size so that an equal partition of nodes is
unlikely between production data centers.
• Through a quorum server, for clusters of any size or type. Quorum
services are provided by a quorum server process running on a
machine outside of the cluster. A single quorum server running on
either HP-UX or Linux can manage multiple HP-UX and Linux
Serviceguard clusters.