Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access for P9000 and XP A.11.00

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 38 (page 103) 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.
• Site 3 is the second-standby site or DC3 for both application A and B.
• The application A is configured using 3DC Sync/CAJ replication. The application B is
configured using 3DC CAJ/CAJ replication.
• For the application A, the data is replicated in a Multi-Target topology from Site 1 to Site 2
and then Site 1 to Site 3. A Delta Resync pair is configured between Site 2 and Site 3.
• For the application B, the data is replicated in a Multi-Target topology from Site 2 to Site 1
and then Site 2 to Site 3. A Delta Resync pair is configured between Site 1 and Site 3.
Figure 38 (page 103) depicts an example of only the applications whose data is being replicated
in a Multi-Target topology. There can also be applications whose data is being replicated in a
Multi-Hop topology.
NOTE: At any point in time, the administrator can change an application’s replication flow to
use different links by interchanging the Delta Resync pair and Active-CAJ pair. For example, if the
replication load is more over the link where Active-CAJ pair is configured, the administrator can
balance the replication load by using a different link to replicate the data to DC3 by interchanging
the Delta Resync pair and Active-CAJ pair. There is no need to change the application’s package
configuration to achieve this.
Bi-Link Configuration
In Bi-Link configuration, for each application, a 3DC replication using two device group pairs is
configured to replicate the data across all its three site as shown in Figure 39 (page 105).
Figure 39 (page 105) depicts an example of Continuous Access link configured between Site1 and
Site3. You can also have Continuous Access link configured between Site2 and Site3 instead of
between Site1 and Site3.
104 Designing a Three Data Center Disaster Recovery Solution