Mirroring terminology

Learn how the mirroring terms apply to your storage array.



Local storage array

The local storage array is the storage array that you are acting upon.

Mirror consistency group

A mirror consistency group is a container for one or more mirrored pairs. For asynchronous mirroring operations, you must create a mirror consistency group. All mirrored pairs in a group are resynchronized simultaneously, thus preserving a consistent recovery point.

Synchronous mirroring does not use mirror consistency groups.

Mirrored pair

A mirrored pair is comprised of two volumes, a primary volume and a secondary volume.

In asynchronous mirroring, a mirrored pair always belongs to a mirror consistency group. Write operations are performed first to the primary volume and then replicated to the secondary volume. Each mirrored pair in a mirror consistency group share the same synchronization settings.

Primary volume

The primary volume of a mirrored pair is the source volume to be mirrored.

Remote storage array

The remote storage array is usually designated as the secondary site, which usually holds a replica of the data in a mirroring configuration.

Reserved capacity

Reserved capacity is the physical allocated capacity that is used for any copy service operation and storage object. It is not directly readable by the host.

These volumes are required so that the controller can persistently save information needed to maintain mirroring in an operational state. They contain information such as delta logs and copy-on-write data.

Secondary volume

The secondary volume of a mirrored pair is usually located at a secondary site and holds a replica of the data.


Synchronization occurs at initial synchronization between the local storage array and the remote storage array. Synchronization also occurs when the primary and secondary volumes become unsynchronized after a communication interruption. When the communication link is working again, any unreplicated data is synchronized to the secondary volume's storage array.