Mirrored aggregates have two copies of their data, called plexes, which use the SyncMirror functionality to duplicate the data to provide redundancy.
When SyncMirror is enabled, all the disks are divided into two disk pools, and a copy of the plex is created. The plexes are physically separated (each plex has its own RAID groups and its own disk pool), and the plexes are updated simultaneously. This provides added protection against data loss if there is a double-disk failure or a loss of disk connectivity, because the unaffected plex continues to serve data while you fix the cause of the failure. Once the plex that had a problem is fixed, you can resynchronize the two plexes and reestablish the mirror relationship.
In the following diagram, SyncMirror is enabled and implemented, so plex0 has been copied and the copy automatically named plex1 by Data ONTAP. Plex0 and plex1 contain copies of one or more file systems. In this diagram, thirty-two disks were available prior to the SyncMirror relationship being initiated. After initiating SyncMirror, the spare disks are allocated to pool0 or pool1.
