Designing Disaster Recovery Clusters using Metroclusters and Continentalclusters, Reprinted October 2011 (5900-1881)

Figure 76 Applications Deployed in a 3DC DR Solution using Tri-Link Configuration
A Continuous Access Synchronous device group pair must be established when using 3DC Sync/CAJ
replication to replicate data between the arrays at the application’s DC1 and DC2 sites. A
Continuous Access Journal device group pair must be established when using 3DC CAJ/CAJ
replication to replicate data between the arrays at the application’s DC1 and DC2 sites. Figure 76
(page 426) depicts both the applications configured using 3DC Sync/CAJ replication and 3DC
CAJ/CAJ replication. You can also have all the applications using only 3DC Sync/CAJ replication
or all the applications using only 3DC CAJ/CAJ replication in a 3DC environment based on your
requirements. Two other Continuous Access Journal pairs, one from the DC1 to DC3 site and
another from DC2 to DC3 site must be created. At any given time, only one of the latter Continuous
Access Journal pairs (DC1-DC3 or DC2-DC3) can be active. So, either the DC1 to DC3 or the
DC2 to DC3 Continuous Access Journal pair must be configured as a Delta Resync pair.
The following terms are used throughout this document to denote these three device groups:
DC1-DC2 pair: The device group pair between DC1 and DC2.
Active-CAJ pair: The Continuous Access Journal device group pair from DC1 or DC2
to DC3 over which the replication is in progress.
Delta Resync pair: The Delta Resync pair configured between DC1 or DC2 and DC3.
If the Active-CAJ pair is configured between DC1 and DC3 then the
Delta Resync pair must be configured between DC2 and DC3.
Similarly, if the Active-CAJ pair is configured between DC2 and DC3
then the Delta Resync pair must be configured between DC1 and
DC3.
In a typical customer DRS environment, more than one application is usually configured to be run
in a Metrocluster/Continentalclusters. Depending on the application distribution in a 3DC
environment, some applications can have Site 1 as its DC1. At the same time, some other
applications can have Site 2 as its DC1. The Delta Resync pair can be configured either between
the application’s DC1 and DC3 or between the application’s DC2 and DC3.
Figure 76 (page 426) depicts an example of two applications distributed in a DRS 3DC environment
balancing the server and replication load. In this example:
• Site 1 is the primary site or DC1 for the application A, and hot-standby site or DC2 for the
application B.
• Site 2 is the primary site or DC1 for the application B, and hot-standby site or DC2 for the
application A.
426 Designing a Three Data Center Disaster Recovery Solution