How Data ONTAP works with MetroCluster configurations
Data ONTAP divides storage across physically separated pools of disks. During configuration, Data ONTAP identifies spare disks and divides them into separate groups called pools. These pools of disks are physically separated from each other, allowing for high availability of mirrored volumes.
When you add a mirrored volume or add disks to one side of a mirrored volume, Data ONTAP determines how much storage you need for the second half of the mirror, and dedicates that storage from a separate pool to the mirrored volume.
Data ONTAP can also be configured to read from both the plexes, which in many cases improves read performance.