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The following table provides definitions for some of the terms that are used in this document.
Term | Definition |
Asynchronous Replication | A replication method which allows you to replicate data over long distances and maintain a replica at a destination site. Updates to the destination image can be issued manually, or automatically based on a customizable Recovery Point Objective (RPO). |
Bandwidth | The amount of data, represented in MB/s, which can be transferred in a given period of time. |
Common Base | A pair of Unified Snapshots taken on a replication source and destination storage resource which have the same point-in-time image. |
Consistency Group (Dell Unity) | A storage instance which contains one or more LUNs within a storage system. Consistency groups help organize the storage allocated for a particular host or hosts. |
Consistency Group (RecoverPoint) | In RecoverPoint, a consistency group is a user-defined group of LUNs to be replicated. A consistency group needs to be created in RecoverPoint as a part of the workflow to configure replication. This consistency group containing Dell Unity LUNs can be replicated locally or remotely. RecoverPoint consistency groups are synonymous with Dell Unity consistency groups. |
Destination Storage Resource | A storage resource that is used for disaster recovery in a replication session. This is also known as a target image. |
Fracture Log | A bitmap held in persistent memory on each storage processor which indicates which physical areas of a source resource participating in a synchronous replication session have been updated since communication was interrupted (fracture). |
Internal Snapshot (Replication Snapshot) | Unified Snapshots created by the system which are part of an asynchronous replication session. These snapshots can be viewed in Unisphere, but user operations are not permitted. Each asynchronous replication session uses two internal snapshots taken on the source and destination storage resources. |
Journal Volume
| In RecoverPoint, a journal volume is a LUN designated to hold data associated with previous points-in-time. The journal is used to allow RecoverPoint to roll back data to any point-in-time. Journal volumes must be configured for each copy of a consistency group, including the production copy. |
LUN | A block-based storage resource which a user provisions. It represents a SCSI logical unit. |
RecoverPoint | An appliance-based disaster recovery solution that replicates synchronously or asynchronously and enables recovery to any point-in-time. |
RecoverPoint Appliance (RPA) | An industry-standard server platform that runs RecoverPoint software and manages all aspects of data protection for a consistency group. RPAs are clustered at each site in a RecoverPoint system for high availability and load balancing. Virtual machines running RecoverPoint software, or vRPAs, are also supported as an alternative to physical appliances. |
Recovery Point Objective (RPO): | The acceptable amount of data, measured in units of time, which may be lost due to a failure. For example, if a storage resource has an RPO of 1 hour, any data written to the storage resource within the most recent hour may be lost when the replication session is failed over to the destination storage resource. |
Recovery Time Objective (RTO): | The duration of time in which a business process must be restored after a disaster. For example, an RTO of 1 hour requires access to the data be restored within 1 hour after a disaster is encountered. |
Replication Session | A relationship configured between two storage resources of the same type, on the same or different systems, to automatically or manually synchronize the data from one resource to another. |
Snapshot | A snapshot, also called a Unified Snapshot, is a point-in-time view of a storage resource. When a snapshot is taken, the snapshot is an exact copy of the source storage resource and shares all blocks of data with it. As data changes on the source, new blocks are allocated and written to. Unified Snapshot technology can be used to take a snapshot of a Block or File storage resource. |
Storage Resource | The top-level object a user can provision, associated with a specific quantity of storage. All host access and data protection activities are performed at this level. In this document, storage resource refers specifically to those which support replication: LUNs, consistency groups, NAS Servers, file systems, and VMware VMFS and NFS Datastores. |
Synchronous Replication | A replication mode in which the host initiates a write to the system at a local site and the data must be successfully stored in both local and remote sites before an acknowledgment is sent back to the host. |
Thin Clone | A thin clone is a Read/Write copy of a Thin Block storage resource (LUN, consistency group, or VMware VMFS datastore) that shares blocks with the parent resource. |
Unisphere | A web-based Dell management interface for creating storage resources and configuring and scheduling protection of stored data on a Dell Unity system. Unisphere can be used for all management of Dell Unity native replication. |
Unisphere for RecoverPoint | A web-based interface for managing RecoverPoint replication. It serves as a single pane of glass for replicating storage resources of multiple storage systems configured to use RecoverPoint. Consistency groups are created, replicated, and recovered through this interface. |
User Snapshot | A snapshot created manually by the user or by a schedule. This is different than an internal snapshot, which is taken automatically by the system with asynchronous replication. |
Write Intent Log | A record stored in persistent memory on the Dell Unity storage system which tracks in-flight writes between systems participating in synchronous replication. |