HP XP Racks - Manual (Page 59)

Figure 19 Example of a 3DC Multi-Target (Cnt Ac-J Z x Cnt Ac-J Z) configuration
Using Continuous Access Journal Z to perform an asynchronous remote copy can reduce the I/O
load on the host. Unlike the 3DC Cascade (Cnt Ac-J Z x Cnt Ac-J Z) configuration, data can be
remotely copied to two sites at the same time without using an intermediate site. This reduces the
time lag of data between sites.
The Delta Resync configuration
The Delta Resync configuration creates a Continuous Access Journal copy pair (Delta Resync pair)
between the local and remote sites in a 3DC Multi-Target (Cnt Ac-S Z x Cnt Ac-J Z) configuration.
Delta Resyncs can be executed to synchronize the Delta Resync pair by copying to the remote site
only the differential data between the local and remote sites. This enables operations to continue
temporarily in a Delta Resync configuration with the local site as the origin with very little downtime,
even when the primary site host stops.
Figure 20 (page 59) gives an example of a Delta Resync configuration before a Delta Resync is
performed, and Figure 21 (page 60) gives an example of a delta resync configuration after a
Delta Resync is performed.
Figure 20 Example of a Delta Resync configuration (before a Delta Resync is performed)
Replication products and data center configurations 59