Active-passive chained replication

In an active/passive chained replication topology, HCP tenants and namespaces and default-namespace directories in one HCP system (A) are replicated to a second HCP system (B) and then from the second system to a third HCP system (C). Both the replication link from A to B and the replication link from B to C are active/passive links.

To configure an active/passive chained replication topology:

1.When you create the replication link from A to B, select the tenants, namespaces, and directories you want to replicate. In this link, A is the primary system and B is the replica.

2.When you create the replication link from B to C, select the link from A to B to be included in that link. This causes the HCP tenants, namespaces, and directories replicated on the link from A to B to be replicated again from B to C. In this link, B is the primary system and C is the replica.

The link from B to C can also include tenants, namespaces, and directories that were originally created on B.

You cannot individually select the replicated tenants, namespaces, and directories on B for inclusion in the link from B to C.

In an active/passive chained replication topology with the configuration ABC, B is the replica for the link from A to B. Therefore, in B, the tenants and directories that were replicated from A are read-only, even though B is also the primary system for the link from B to C.

HCP supports replication chains that consist of three HCP systems. Longer chains are not supported.

Note:  

You can also create a chained replication topology in which the first link is active/active and the second link is active/passive. You cannot, however, create a chained replication topology in which the first link is active/passive and the second link is active/active or in which both links are active/active.

In a replication chain ABC in which the objects in a namespace on system B are supposed to be metadata-only, HCP does not remove data from those objects until that data has been replicated to system C. For information on metadata-only objects, see Administering HCP.

What this looks like

The figure below shows an active/passive chained replication topology in which system A is replicating to system B and system B is replicating to system C.

In this figure:

From system A, two HCP tenants are being replicated to system B. In the first tenant, two of three namespaces are selected for replication. In the second tenant, one of two namespaces is selected for replication.

From system B, the tenants and namespaces created by replication from system A are being replicated to system C because the link from A to B is included in the link from B to C.

One tenant that was originally created on system B is also being replicated to system C. Both the namespaces in that tenant are selected for replication.

Uses

In an active/passive chained replication topology, all three HCP systems are typically located at full-scale data centers. For example, suppose a corporation has three major locations — New York, Los Angeles, and Tokyo. Each of these locations runs an application that is vital to the corporation, but only New York generates the data for these applications. Replicating the data from New York to Los Angeles and from Los Angeles to Tokyo enables applications at each location to access the data through a local area network. Because those applications are not accessing the data on the HCP system in New York, this topology also reduces the load on that system.

Active/passive chained replication helps ensure continuous data availability. If any one or even two of the HCP systems in the chain become unavailable, applications still have access to the stored data.

In an active/passive replication chain, the third HCP system provides disaster recovery functionality for the second system, and the second system provides disaster recovery functionality for the first system. For information on data recovery in an active/passive chained replication topology, see Failover and failback in an active-passive chained topology.

In an active/passive chained replication topology, you can create and manage both replication links from the HCP system in the middle of the chain. To this system, the link from the first system is an inbound link, and the link to the third system is an outbound link.

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