content_image/976088.jpg content_image/976089.jpg
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: 

GLYPH<SM590000> Larger RPO 

GLYPH<SM590000> Point-in-time copies 

GLYPH<SM590000> Asynchronous 

GLYPH<SM590000> Possible system performance resource requirements because point-in-time copies are created locally 

Figure 11-92 shows a simple Global Mirror relationship without Change Volumes. 

<img src='content_image/976088.jpg'>

With Change Volumes, this environment looks as it is shown in Figure 11-93. 

<img src='content_image/976089.jpg'>

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 - 1 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 460. 

