Understanding Data Replication

Data replication is the copying of data from a primary storage device to a backup or secondary device. If the primary device fails, your data is available from the secondary device. In this way, data replication helps assure high availability and disaster tolerance for your cluster.

Sun Cluster supports the following approaches to data replication:

• Host-based data replication uses special software to replicate disk volumes between geographically dispersed nodes in real time. Remote mirror replication enables data from the master volume of the primary node to be replicated to the master volume of the geographically dispersed secondary node. A remote mirror bitmap tracks differences between the master volume on the primary disk and the master volume on the second disk.

  Host-based data replication is a less expensive data replication solution because it does not require storage arrays. Host-based data replication uses locally-attached disks. However, host-based data replication uses host resources to perform data replication and does not support scalable applications like Oracle RAC. For more information about using host-based data replication in a campus cluster environment, see Using Host-Based Data Replication . For more information about using host-based data replication between two or more clusters, see Sun Cluster Geographic Edition Data Replication Guide for Hitachi TrueCopy.

• Storage-based data replication uses special software to move the work of data replication off the cluster nodes and onto the storage device. This software relocation frees some node processing power to serve cluster requests. Storage-based data replication can be especially important in campus cluster configurations because this type of data replication supports scalable applications and offloads the hosts. Also, storage-based replication supports scalable applications such as Oracle RAC. For more information about using storage-based data replication in a campus cluster environment see Using Storage-Based Data Replication. For more information about using storage-based replication between two or more clusters and the Sun Cluster GeoEdition product that automates the process, see Sun Cluster Geographic Edition Data Replication Guide for Sun StorageTek Availability Suite.

Sun StorageTek Availability Suite software provides a mechanism for host-based data replication across geographically distant clusters. Example: Configuring Host-Based Data Replication With Sun StorEdge Availability Suite or Sun StorageTek Availability Suite Software at the end of this chapter provides a complete example of such a cluster configuration.