Figure 6-17 shows a colliding write sequence. Figure 6-17 Colliding writes The following numbers correspond to the numbers that are shown in Figure 6-17: The first two actions (1 and 2) occur asynchronously with the first write. 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. Global Mirror Change Volumes functional overview 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. 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. ‘ 176  IBM FlashSystem 9200 and 9100 Best Practices and Performance Guidelines