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Dell Unity’s Native Synchronous Block Replication feature is supported in two different topologies, and deployment models will vary depending on the requirements of the configuration. The following synchronous replication topologies outline the system configuration options supported in Dell Unity.
The following figure, Figure 3, is a graphical view of the supported topologies listed above. Note the figure uses LUNs as an example. For synchronous replication, the source and destination system must be a physical system, but the models used can vary depending on the configuration requirements. Below are examples of the two topologies that can be used, either One-Directional or Bi-Directional replication. The source and destination system can either be the same model type, either All Flash or Hybrid, or the source and destination can be a mix of different model All Flash and Hybrid systems.
Figure 3. Supported synchronous block replication topologies
One-Directional replication is typically deployed when only one of the systems will be used for production I/O. The second system is a replication target for all production data and sits idle within the same data center or a remote location. If the need arises, the DR system can be placed into production and host production I/O. In this scenario, mirroring the production system’s configuration, including the number of drives and Pool layout, on the DR system is suggested, as each system would then have the same performance potential.
The Bi-Directional replication topology is typically used when production I/O needs to be spread across multiple systems or locations. The systems may exist within a single data center or in different, remote locations. When using this replication topology, production I/O from each system is mirrored to the peer system. If there is an outage, one of the systems can be promoted as the primary production system, and all production I/O can be sent to it. Once the outage is complete, the replication configuration can be changed back to its original configuration. This replication topology ensures both systems are in use by production I/O at all times.
On Dell Unity, a block resource can only be synchronously replicated to one single storage resource on a remote system. This means that replicating a single storage resource to multiple destination resources is not supported. Therefore, only one replication connection between a source and destination pair of Dell Unity systems can be used for synchronous replication. Cascading replication, when a destination storage resource is also replicated to another destination resource, is also not supported for synchronous block replication.