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

Table 31 Difference Between 3DC Sync/CAJ and 3DC CAJ/CAJ Replication (continued)
3DC CAJ/CAJ replication3DC Sync/CAJ replication
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 417).
In a Tri-Link configuration there are three Continuous Access replication links configured as shown
in Figure 63 (page 414). 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
data replication is established to replicate data between the arrays at Site1 and Site2 when
using 3DC CAJ/CAJ replication.
• Continuous Access Journal data replication must be established between one of the arrays
located in the Metrocluster - Site1 or Site2 - and the array located at Site3. This replication
pair is used to replicate data to Site3 actively and will be referred as Active-CAJ pair.
• A Delta Resync pair is configured over the remaining data replication link between Site1 or
Site2 and the array located at Site3. The Delta Resync pair is a suspended journal volume,
which can be resynchronized to replicate data to Site3 in case of data not being replicated
to Site3 using the Active-CAJ pair. If the Active-CAJ pair is configured between Site1 and
Site3 then the Delta Resync pair must be configured between Site2 and Site3. Similarly, if the
Active-CAJ pair is configured between Site2 and Site3 then the Delta Resync pair must be
configured between Site1 and Site3.
In a Bi-Link configuration, there are two Continuous Access replication links configured. A replication
link is configured between Site1 and Site2 of Metrocluster and another replication link is configured
either between Site1 and Site3 or between Site2 and Site3.
Figure 64 (page 416) shows the Bi-Link configuration with the replication link configured between
Site1 and Site3.
Overview of 3DC DR Solution 415