Key terminology

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As you begin to explore the ONTAP SnapMirror Business Continuity and plan a deployment, it is helpful to become familiar with the key terminology and concepts.

SM-BC

Acronym for the SnapMirror Business Continuity (SM-BC) solution available with ONTAP 9.8 and later.

Consistency group

A consistency group (CG) is a collection of FlexVol volumes that provide a write order consistency guarantee for the application workload which needs to be protected for business continuity. The purpose of a consistency group is to take simultaneous crash-consistent Snapshot copies of a collection of volumes at a point in time. In regular deployment, the group of volumes picked to be part of a CG are mapped to an application instance. SnapMirror relationships, also known as a CG relationship, is established between a source CG and a destination CG. The source and destination CGs must contain the same number and type of volumes.

Constituent

The individual FlexVol volumes that are part of a consistency group.

Mediator

External software installed in a standalone server or in a VM. It is a monolithic process that is required to complete a quorum for SM-BC deployment. Mediator is used for health checking and to establish a consensus across a 3-party quorum where the other two parties are the two clusters hosting the SM-BC primary CG and mirror CG copies. Both are used interchangeably.

Out of Sync (OOS)

The application I/O is not replicating to the secondary storage system. The destination volume is not in sync with the source volume because SnapMirror replication is not occuring. If the mirror state is Snapmirrored, this indicates a transfer failure or failure due to an unsupported operation.

Zero RPO

Zero recovery point objective. This is the acceptable amount of data loss from downtime.

Zero RTO

Zero recovery time objective or Transparent Application Failover is achieved by using host multipath I/O (MPIO) software-based path failover to provide non-disruptive access to the storage.