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. enables connectivity between Fibre Channel initiators and SAS
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 the following plexes:
The local plex (on the local shelf) that is actively serving data
The remote plex (on the remote shelf) that is normally not serving data
On local shelf failure, the remote shelf seamlessly takes over data-serving operations. Both
copies or plexes are updated synchronously on writes, which ensures consistency.

8.5.1 SyncMirror overview

The design of IBM System Storage N series and MetroCluster provides data availability even
if there is 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.
Read performance is optimized by performing application reads from both plexes, as shown
in Figure 8-9 on page 115.
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IBM System Storage N series Hardware Guide