In a replicated data cluster there is no shared disk. Instead, a data replication product synchronizes copies of data between nodes. Replication can take place at the application, host, and storage levels. Application-level replication products, such as Oracle DataGuard, maintain consistent copies of data between systems at the SQL or database levels. Host-based replication products, such as Veritas Volume Replicator, maintain consistent storage at the logical volume level. Storage- or array-based replication maintains consistent copies of data at the disk or RAID LUN level.
The following illustration shows a hybrid shared storage/replicated data cluster, in which different failover priorities are assigned to nodes according to particular service groups.
Shared storage replicated data cluster
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Replicated data clusters can also be configured without the ability to fail over locally, but this configuration is not recommended.