Chapter 11. Advanced Copy Services 529
Your change rate needs to include only the condition of the data at the point-in-time that the 
image was taken, rather than all the updates during the period. The use of this function can 
provide significant reductions in replication volume. 
Global Mirror with Change Volumes has the following characteristics:
/SM590000Larger RPO
/SM590000Point-in-time copies
/SM590000Asynchronous
/SM590000Possible system performance resource requirements because point-in-time copies are 
created locally
Figure 11-92 shows a simple Global Mirror relationship without Change Volumes.
Figure 11-92   Global Mirror without Change Volumes
With Change Volumes, this environment looks as it is shown in Figure 11-93. 
Figure 11-93   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 in 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. 
For more information about IBM FlashCopy, see 11.1, “IBM FlashCopy” on page 436.