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There are two main strategies to implement a disaster recovery or high availability for stateful applications. You can rely of the application to synchronize the data, or you can use volume-level replication.
Certain applications, such as Elasticsearch, Cassandra, and Couchbase, replicate their data natively between an odd number of nodes, while transactional databases such as PostgreSQL and MySQL often use a primary/stand-by approach.
With volume-level replication, the storage backend manages the replication of the data between different sites. In the case of PowerMax, Symmetrix Remote Data Facility (SRDF) manages the replication. The application can then access data from either of the replicated sites.
CSI and CSM for PowerMax support three replication types: asynchronous, synchronous, or active/active replication with SRDF metro. Geographical and availability requirements dictate which replication mode is best suited to the needs of the application being replicated.