IBM Storwize V5010 Manual page 595

Figure 10-84 shows a simple Global Mirror relationship without Change Volumes.
Figure 10-84 Global Mirror without Change Volumes
With Change Volumes, this environment looks as it is shown in Figure 10-85.
Figure 10-85 Global Mirror with Change Volumes
With Change Volumes, a FlashCopy mapping exists between the primary volume and the
primary Change Volume. The mapping is updated on the cycling period (60 seconds to one
day). The primary Change Volume is then replicated to the secondary Global Mirror volume at
the target site, which is then captured in another Change Volume on the target site. This
approach provides an always consistent image at the target site and protects your data from
being inconsistent during resynchronization.
Figure 10-86 shows how Change Volumes might save you replication traffic.
Figure 10-86 Global Mirror I/O replication without Change Volumes
573
Chapter 10. Copy services