HCP System Management Help


How replication works

To start the replication service, you create a replication link between the local system and another HCP system. A replication link is a secure trust relationship between the two systems. It determines what is replicated and how data is transmitted between the systems.

Link types

A replication link can be an active/active or active/passive:

With an active/active link, the HCP tenants and namespaces and default-namespace directories being replicated are read-write on both systems, and data is replicated in both directions between the two systems. Active/active links are designed for use in a cloud storage environment, where applications need seamless access to namespaces regardless of where those applications are located.

With an active/active link, HCP gives preference to synchronizing object metadata between the two systems, followed by data synchronization. This preferential treatment enables the fastest access to objects regardless of which system they were created on. If the data for an object has not yet been replicated to the system targeted by a client request, HCP can read the data from a remote system. Additionally, synchronizing metadata first ensures that object names are reserved as quickly as possible.

Note: Until the data for an object is replicated to a given system, the object is metadata-only on that system.

With an active/passive link, the HCP tenants and namespaces and default-namespace directories being replicated are read-write on one system, called the primary system, and read-only on the other system, called the replica. In this case, data is replicated in one direction only — from the primary system to the replica. Active/passive links are designed to support disaster recovery.

With an active/passive link, HCP replicates object data and metadata together, thereby ensuring that objects are intact on the replica and can be recovered as whole objects should that become necessary. However, this approach to object replication means that the replica cannot service requests for any given object until that object is fully replicated.

To a primary system, an active/passive link is an outbound link; that is, the system is sending data through the link. To a replica, an active/passive link is an inbound link; that is, the system is receiving data through the link. To either system involved in an active/active link, the link functions as both an outbound link and an inbound link.

Link security

Replication relies on SSL to ensure the integrity and security of transmitted data. Before you can create a replication link, each system involved in the link must each have a valid SSL server certificate. Each system must also have the server certificate from the other system installed as a trusted replication server certificate.

Replication priority

Replication is asynchronous with other tenant and namespace activity on both systems involved in a link. An HCP system can, therefore, develop a backlog of objects to be replicated.

You can choose to have the replication service work on objects with the oldest changes first, regardless of which namespaces they’re in. Alternatively, you can have the service balance its processing time evenly across the namespaces being replicated. In this case, the service may replicate recent changes in some namespaces before older changes in others.

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