Synchronous Mirroring With Syncmirror; Syncmirror Overview - IBM N Series Hardware Manual

This process allows SAS disks to display as LUNs in a MetroCluster fabric. You need at least
four FibreBridges (minimum is two per stack) in a MetroCluster environment as shown in
Figure 8-8.
Figure 8-8 Cabling a Fabric MetroCluster with FibreBridges and SAS Shelves
For more information about SAS Bridges, see the SAS FibreBridges Chapter in the N series
Hardware book.

8.5 Synchronous mirroring with SyncMirror

SyncMirror synchronously mirrors data across the two halves of the MetroCluster
configuration by writing data to two plexes:
The local plex (on the local shelf) actively serving data
The remote plex (on the remote shelf) normally not serving data
On local shelf failure, the remote shelf seamless takes over data-serving operations. Both
copies or plexes are updated synchronously on writes, thus ensuring consistency.

8.5.1 SyncMirror overview

The design of IBM System Storage N series and MetroCluster provides data availability even
in the event of an outage. Availability is preserved whether it is because of a disk problem,
cable break, or host bus adapter (HBA) failure. SyncMirror can instantly access the mirrored
data without operator intervention or disruption to client applications.
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IBM System Storage N series Hardware Guide