Continental Clusters

Arbitration for Data Integrity in Serviceguard Clusters

Arbitration in Disaster-Tolerant Clusters

There are no special arbitration requirements or configurations for the separate clusters within a continental cluster. Each cluster must provide its own arbitration separately, according to the applicable rules for a standard Serviceguard cluster. In other words, the continental cluster can employ any supported method of arbitration for its component clusters.

ContinentalClusters provides semi-automatic failover via commands which must be issued by a human operator. Between the member clusters of a continental cluster, the arbitrator is the system administrator on the recovery site, who must verify that it is appropriate to issue the cmrecovercl command.

Use of Dual Lock Disks in Extended Distance Clusters

Lock disks are not supported in metropolitan clusters, but they can be used in an extended distance cluster, which employs mirrored LVM over a FibreChannel disk link.

NOTE	Dual lock LUN configurations are not supported.

For an extended distance cluster, there should be one lock disk in each of the data centers; all nodes have access to both lock disks via the disk link. In the event of a failure of one of the data centers, the nodes in the remaining data center will be able to acquire their local lock disk, allowing them to successfully reform a new cluster. In a dual lock disk configuration, there is an extremely slight chance of split-brain in dual lock disk configuration.

The use of dual locks is as follows in an extended distance cluster:

1.After the loss of heartbeat between the data centers, each sub-cluster attempts to access the first lock disk, then the second lock disk.

2.If a node in one data center is successful at obtaining the first lock disk and the disk link between the two data centers is still viable, then nodes in the second data center will be refused the lock. The first data center will then be able to obtain the second disk and re-form the cluster.