IBM XIV Storage System Copy Services and Migration

Dependent writes: normal operationApplications or databases often manage dependent write consistency using a 3-step processsuch as the sequence of three writes shown in Figure 4-30. Even when the writes aredirected at different logical volumes, the application ensures that the writes are committed inorder during normal operation.2) Update RecordDB1) Intend to update DB3) DB updatedLogFigure 4-30 Dependent writes: normal operationDependent writes: failure scenarioIn the event of a failure, applications or databases manage dependent writes, as shown inFigure 4-31. If the database record is not updated (step 2), the application does not allow DBupdated (step 3) to be written to the log.x2) Update RecordDB1) Intend to update DB3) DB updatedLogFigure 4-31 Dependent writes: failure scenarioJust as the application or database manages dependent write consistency for the productionvolumes, the XIV system must manage dependent write consistency for the mirror targetvolumes.Chapter 4. Remote Mirroring 95