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Storage : Aggregates : Understanding aggregates : How mirrored aggregates work
How mirrored aggregates work
Mirrored aggregates have two plexes (copies of their data), which use the SyncMirror functionality to duplicate the data to provide redundancy.
When SyncMirror is enabled, all the disks or array LUNs are divided into two pools, and a copy of the plex is created. The plexes are physically separated (each plex has its own RAID groups and its own pool), and the plexes are updated simultaneously. This provides added protection against data loss if more disks fail than the RAID level of the aggregate protects against or there is a loss of connectivity, because the unaffected plex continues to serve data while you fix the cause of the failure. After the plex that had a problem is fixed, you can resynchronize the two plexes and reestablish the mirror relationship.
Note: Before an aggregate can be enabled for mirroring, the storage system must have the syncmirror_local license installed and enabled, and the storage configuration must support RAID-level mirroring.
In the following diagram of a storage system using disks, SyncMirror is enabled and implemented, so Data ONTAP copies plex0 and automatically names the copy plex1. Plex0 and plex1 contain copies of one or more file systems. In this diagram, 32 disks were available prior to the SyncMirror relationship being initiated. After initiating SyncMirror, the spare disks are allocated to pool0 or pool1.
The following diagram shows a storage system using array LUNs with SyncMirror enabled and implemented.

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