HCP has these features that help ensure the continuous availability of stored data:
•Multipathing — In a SAIN system, a single node can connect to more than one port on a storage array, either directly or through multiple Fibre Channel switches. This creates multiple physical paths between the node and any given logical volume that maps to it. With this setup, if one component of a physical path connecting such a node to the array fails, the node still has access to the logical volume through another physical path.
Multiple means of access to a logical volume from a single node is called multipathing.
•Zero-copy failover — In a SAIN system, one node can automatically take over management of storage previously managed by another node that has failed. This process is called zero-copy failover.
To support zero-copy failover, each logical volume that stores objects or the metadata query engine index must map to two different storage nodes. The pair of nodes forms a set such that the volumes that map to one of the nodes also map to the other. This is called cross-mapping.
For more information on zero-copy failover and cross-mapping, see Zero-copy failover behavior.
•Service plans — Each namespace has a service plan that defines both a data protection strategy and a storage tiering strategy for the objects in that namespace. At any given point in the lifecycle of an object, its data protection strategy specifies the number of copies of the object that must exist in the HCP repository and the type of storage on which each copy must be stored.
Because some types of storage are more highly available than others, you can use the service plan for a namespace to control both data redundancy and data availability for the objects in that namespace.
For more information on using service plans to define a data protection strategy for objects in a namespace, see About service plans.
•Protection service — HCP uses the protection service to maintain the correct number of copies of each object in the HCP repository. When the number of existing copies of an object goes below the number of object copies specified in the applicable service plan (for example, because of a logical volume failure), the protection service automatically creates a new copy of that object in another location. When the number of existing copies of an object goes above the number of object copies specified in the applicable service plan, the protection service automatically deletes all unnecessary copies of that object.
For more information on the protection service, see Protection service.
•Protection sets — To protect data availability against concurrent node failures, HCP stores multiple copies of each object on different nodes in an automatically predetermined set of nodes, called a protection set. If a node (or one of its logical volumes) fails, objects stored on its associated volumes (or on the failed volume) are still available through other nodes in the set.
For information on protection sets, see Ingest tier data protection level.
•Replication — Replication is the process of keeping two or more HCP systems in sync with each other. The replication service on each system automatically copies selected HCP tenants and namespaces and default-namespace directories to one or more of the other systems to form a replication topology. Both configuration information and namespace content are copied.
Replication enables HCP to support a cloud storage model, where any type of client request can be serviced equally by any system in the topology. If the systems are in geographically disperse locations, each system may be able to provide faster data access for some applications than the other systems can, depending on where the applications are running.
If a system in a replication topology fails, other systems in the topology can both provide continued namespace availability and serve as sources for disaster recovery.
For more information on replication, see Replicating Tenants and Namespaces.
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Note: Replication is an add-on feature to HCP. If your HCP system doesn’t include this feature and you would like to add it, please contact your HCP sales representative. |
•Read from remote — If an object in a replicated HCP namespace or default-namespace directory is unavailable on one system in a replication topology (for example, because a node is unavailable), HCP can try to read the object from another system in the topology. HCP tries this only if the namespace has the read-from-remote feature enabled and the object has already been replicated.
For information on enabling the read-from-remote feature for a namespace, see Managing a Tenant and Its Namespaces or Managing the Default Tenant and Namespace.
•Automatic redirection to other systems in a replication topology — HTTP requests for access to an unavailable HCP system can be automatically redirected to any other system in a replication topology in which the unavailable system participates. This means that, to be satisfied, the request does not need to be reissued with a different URL.
For another system to satisfy the request, the target HCP namespace or default-namespace directory must be replicated to that system. Also, the namespace must be configured to accept requests directed to other HCP systems. Additionally, the DNS must be configured to support redirection between HCP systems in the replication topology, and the unavailable system must be configured to allow this redirection.
For information on:
oConfiguring namespaces to accept requests directed to other systems, see Managing a Tenant and Its Namespaces or Managing the Default Tenant and Namespace
oConfiguring HCP in your DNS, see Configuring DNS for HCP
oConfiguring an HCP system to support redirection of client requests, see Replicating Tenants and Namespaces
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