For array LUN aggregates, SyncMirror creates two physically separated copies of the aggregate, just as it does for disks.
These copies of the aggregate, called plexes, are simultaneously updated; therefore, the two copies of the data are always identical. Data continues to be served if one copy becomes unavailable.
For array LUNs, the physical separation of the plexes protects against data loss if the following occurs:
For example, a LUN failure can occur because of a double disk failure on the storage array.
The entire site might fail because of a disaster or prolonged power failure. If this situation occurs, the surviving site can take over the functions of the disaster site as a result of a switchover. Data is accessed on the plex of the surviving site.
Each of the two plexes must be on a separate set of array LUNs. In a MetroCluster configuration with Data ONTAP systems that use array LUNs, each plex must be on a separate set of LUNs on different storage arrays. For MetroCluster configurations with Data ONTAP systems that use both array LUNs and disks, the plexes for disks are separate from the plexes for array LUNs.
When SyncMirror is used in a setup other than a MetroCluster configuration, each of the plexes can be on the same storage array or on different storage arrays.
Plexes can be considered local or remote in the context of the storage array that is connected to the Data ONTAP system on which the aggregate is configured. For example, in MetroCluster configurations, the plex at the local site is the local plex while the one at the remote site is the remote plex.
The following illustration shows the relationships of plexes and pools to an aggregate. One plex is associated with pool 0 and one plex is associated with pool 1. The local pool is pool 0 while the remote pool is pool 1. The remote plex is the mirror of the aggregate.