content_image/968972.jpg
Figure 6-17 shows a colliding write sequence. 

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<img src='content_image/968972.jpg'>

The following numbers correspond to the numbers that are shown in Figure 6-17: 

1. A first write is performed from the host to LBA X. 

2. A host is provided acknowledgment that the write is complete, even though the mirrored write to the auxiliary volume is not yet completed. 

The first two actions (1 and 2) occur asynchronously with the first write. 

3. A second write is performed from the host to LBA X. If this write occurs before the host receives acknowledgment (2), the write is written to the journal file. 

4. A host is provided acknowledgment that the second write is complete. 

## Global Mirror Change Volumes functional overview 

Global Mirror with Change Volumes (GM/CV) provides asynchronous replication based on point-in-time copies of data. It is designed to allow for effective replication over lower bandwidth networks and to reduce any impact on production hosts. 

Metro Mirror and Global Mirror both require the bandwidth to be sized to meet the peak workload. Global Mirror with Change Volumes must only be sized to meet the average workload across a cycle period. 

