Editing Write Anywhere File Layout (section)

===Plexes===
[[File:MetroCluster replication diagram.png|thumb|SyncMirror replication using plexes]]
Similar to [[RAID 1]], plexes in ONTAP systems can keep mirrored data in two places, but while conventional RAID-1 must exist within the bounds of one storage system, two plexes could be distributed between two storage systems. Each [[ONTAP#Aggregates|aggregate]] consists of one or two plexes. Conventional HA storage systems have only one plex for each aggregate, while SyncMirror local or MetroCluster configurations can have two plexes for each aggregate. On the other hand, each plex includes underlying storage space from one or more NetApp [[NetApp FAS#RAID|RAID groups]] or LUNs from third-party storage systems (see [[NetApp FAS#FlexArray|FlexArray]]) in a single plex similarly to [[RAID 0]]. If an aggregate consists of two plexes, one plex is considered a master and second as a slave; slaves must consist of exactly the same RAID configuration and drives. For example, if we have an aggregate consisting of two plexes where the master plex consists of 21 data and 3 1.8 TB SAS parity drives in RAID-TEC, then the slave plex must consist of 21 data and 3 1.8 TB SAS parity drives in RAID-TEC. The second example, if we have an aggregate consisted of two plexes where master plex consists of one RAID 17 data and 3 parity SAS drives 1.8 TB configured as RAID-TEC and second RAID in the master plex is RAID-DP with 2 data and 2 parity SSD 960 GB. The second plex must have the same configuration: one RAID 17 data and 3 parity SAS drives 1.8 TB configured as RAID-TEC, and the second RAID in the slave plex is RAID-DP with 2 data and 2 parity SSD 960 GB.
[[NetApp FAS#Metro Cluster|MetroCluster]] configurations use SyncMirror technology for synchronous data replication. There are two SyncMirror options: MetroCluster and Local SyncMirror, both using the same plex technique for synchronous replication of data between two plexes. Local SyncMirror creates both plexes in a single controller and is often used for additional security to prevent failure for an entire disk shelf in a storage system. MetroCluster allows data to be replicated between two storage systems. Each storage system could consist of one controller or be configured as an HA pair with two controllers. In a single HA pair, it is possible to have two controllers in separate chassis and distance from each other could be tens of meters, while in MetroCluster configuration distance could be up to 300&nbsp;km.