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

9 Designing a Three Data Center Disaster Recovery Solution
This chapter describes Three Data Center architecture through the following topics:
NOTE: For additional information, see the Release Notes for your Metrocluster and
Continentalclusters products and the documentation for your storage solution.
Overview of Continuous Access 3DC Replication Technology
The Continuos Access 3DC replication can be configured using either 3DC Sync/CAJ replication
or 3DC CAJ/CAJ replication. Here CAJ refers to Continuous Access Journal. In 3DC Sync/CAJ
replication, the replication between the sites located in Metrocluster is synchronous and configured
using Continuous Access Synchronous device group pair where as in 3DC CAJ/CAJ replication,
the replication between the sites located in Metrocluster is asynchronous and configured using
Continuous Access Journal replication device group pair. For information regarding CAJ, see HP
StorageWorks P9000 Continuous Access Journal Software User Guide or HP StorageWorks
XP24000/XP20000 Continuous Access Journal Software User Guide available at
nl
http://h20000.www2.hp.com/bizsupport/TechSupport/Home.jsp.
Table 10 Difference Between 3DC Sync/CAJ and 3DC CAJ/CAJ Replication
3DC CAJ/CAJ replication3DC Sync/CAJ replication
The replication between the sites in a Metrocluster is
asynchronous using Continous Access Journal replication
available in StorageWorks XP and P9000 Storage Arrays.
The replication between the sites in a Metrocluster is
synchronous.
Data may be lagging at the other site in the Metrocluster.Highest level of data currency is maintained at the other
site in the Metrocluster.
Performance of the application is not impacted due to the
replication between the sites in the Metrocluster.
Performance of the application may be impacted due to
the synchronous replication between the sites in the
Metrocluster. This depends on workload, intersite link
bandwidth provisioned and read/write ratio amongst other
factors.
Suitable for the write-intensive applications where the
performance with synchronous replication can not be
sustained.
Suitable for applications where data currency is more
important and the performance can be sustained.
Comparatively lower cost for inter site links as it can work
with even high latency and low bandwidth.
Higher cost for inter site links in Metrocluster as it requires
low latency and high bandwidth.
The 3DC Sync/CAJ and 3DC CAJ/CAJ replications can coexist in the 3DC DR Solution for different
applications. Both 3DC Sync/CAJ and 3DC CAJ/CAJ replication can be implemented with either
two or three links between the three data centers. The two link configuration is called as Bi-Link
and the three link configuration is called as Tri-Link. Users can decide the replication for an
application based on their requirements. For pros and cons of using Bi-Link and Tri-link configuration,
see “Pros and Cons of Using Bi-Link and Tri-Link Configuration” (page 93).
In a Tri-Link configuration there are three Continuous Access replication links are configured. A
replication link is configured between Site1 and Site2 of Metrocluster and another two links are
configured between each site (Site1 and Site2) of Metrocluster to far-site, Site3. In Tri-Link
configuration:
• Continuous Access Synchronous data replication is established to replicate data between the
arrays at Site1 and Site2 when using 3DC Sync/CAJ replication. Continuous Access Journal
Overview of Continuous Access 3DC Replication Technology 91