Remote-copy relationships

Metro Mirror, Global Mirror, and active-active (HyperSwap®) relationships define the relationship between two volumes: a master volume and an auxiliary volume. Active-active relationships are created automatically when a HyperSwap volume is created in either the management GUI or the command line interface.

Typically, the master volume contains the production copy of the data and is the volume that the application normally accesses. The auxiliary volume typically contains a backup copy of the data and is used for disaster recovery.

The master and auxiliary volumes are defined when the relationship is created, and these attributes never change. However, either volume can operate in the primary or secondary role as necessary. The primary volume contains a valid copy of the application data and receives updates from the host application, analogous to a source volume. The secondary volume receives a copy of any updates to the primary volume because these updates are all transmitted across the mirror link. Therefore, the secondary volume is analogous to a continuously updated target volume. When a relationship is created, the master volume is assigned the role of primary volume and the auxiliary volume is assigned the role of secondary volume. Therefore, the initial copying direction is from master to auxiliary. When a Metro Mirror or Global Mirror relationship is in a consistent state, you can reverse the copy direction.

Usually, the two volumes in a relationship must be the same size.

For ease of application management, a relationship can be added to a consistency group.