Preservation Service

The Preservation service (depicted in Figure 1) handles the data preservation, replication, and archival/backup of the DM subsystem and represents a critical part of the CI.

Figure 1 Preservation Service (OV-2)

The History service acts as a data broker for preservation service. It identifies and delegates the data access (read/write) request to the right sub-service based on the requested data product, its direction (to or from the preservation service), and the origin and destination of data (e.g., in between facilities or inside a single facility). For instance, a request for storage of a particular data stream may go to the replication and local archival services at the same time; similarly, a "not-found" message from a local archive may trigger a "locate" message to the replication service through the history service to identify other replicas of the requested data.

The Replication service performs data replication through the federated system of facilities. This service provides the foundation for the distributed storage mechanisms offered by the preservation service.

From the perspective of the Cache service, the purpose of replication is to provide high speed availability of data in the physical installations of the CI subject to OOI policy.

From the perspective of the Backup service, the purpose of replication is to provide a mechanisms to safe guard against information loss due to failure in a component or an installation of the system.

The Long Term Archive service provides backup medium for indefinite offline storage as dictated by the OOI data retention policies. It provides the means for restoring original content in case of critical failures in the CI or any of its subsystems at both the level of data/metadata and algorithms/applications.

The Persistent Archive service provides the access to the file system. In a deployed facility, it will reflect the local storage capabilities directly accessible to any subsystem service running on that physical node (e.g., local disk, NAS, SAS, or a federated file system). For deployment in a federated system the Persistent Archive service realizes access to and policy management of the virtual file system.

Figure 2 Persistent Archive (OV-2)