Replication
With Advanced storage area content replication, multiple replicas can be defined within a site or across sites (remote sites). An advanced storage area replicates synchronously to a designated number of storage devices in a designated priority order. The advanced storage area selects which storage devices to use for synchronous replication based on the available devices and their synchronization type (primary, secondary, or asynchronous). Until the specified number of synchronous replicas is reached, primary storage devices are selected first, followed by secondary storage devices. Within each primary or secondary designation, a storage device at the local site has a higher priority than one at a remote site.
Designations can also be customized with site overrides. For example, in one site a replica can be designated as primary, but in a different site, where access to that replica is over a slow connection, it can be designated as secondary or asynchronous.
For content upload, if the number of required replicas is not successfully written, the document creation fails. For content download, an advanced storage area performs automatic failover to a redundant copy of the content if the content cannot be retrieved from the higher priority replica.
Replicating to a remote site
To replicate to a remote site, the local server instance forwards a content transfer request to the remote server instance, which is responsible for uploading the content it receives to each of the selected replicas in its site. This type of communication between two Content Platform Engine servers is referred to as Content Platform Engine server communication. If the remote server is inaccessible to the local server instance, then the local instance attempts to write the content directly to the targeted replicas in the remote site.
It is a requirement that an instance of Content Platform Engine has direct connectivity to all replicas within the site of the instance. For a server instance that replicates to storage devices on a remote site, it is also a requirement that the instance has either direct connectivity to all of the storage devices in the remote site or is configured for Content Platform Engine server communication to that site.
Asynchronous replication
Content can also be written to replicas asynchronously with the content replication request sweep. Asynchronous replication is used under the following conditions:
- A storage device connection for a replica is explicitly configured for asynchronous replication.
- Because of the way replication is configured in an advanced storage area, there is no need to synchronously replicate to a primary or secondary designated device. For example, if the maximum number of synchronous replicas has already been reached, but there are other primary or secondary designated replicas available, then, for performance purposes, the advanced storage area writes asynchronously to the remaining replicas.
- A synchronous write attempt to a replica fails. For example, if a primary replica fails, but the required number of primary replicas is satisfied, the advanced storage area places the write request to the failed replica in the replication sweep queue. The replication queue sweep writes the content after the failed replica is restored.