HP 418800-B21 HP StorageWorks Replication Solutions Manager 4.0.1 user guide ( - Page 105

Log contents A small portion of log space is reserved for array commands. The largest portion stores host data that is written to all of the virtual disks in the disk group. Log and disk group planning When you create a DR group pair, a log disk is automatically created for the source and destination DR group. An important planning factor is selecting the disk groups in which to create the log disks. Disk group category • Select a disk group whose category is appropriate to the write mode of the DR group pair. See write mode and online and near-online disk groups. You can use HP Command View EVA to determine the category the disk groups that are displayed in the replication manager. Write mode Recommended disk group category Enhanced asynchronous online Standard asynchronous near-online Synchronous near-online • If near-online disk groups cannot be made available, use the online disk groups that have the most free space. Disk group size • When selecting a disk group, ensure there is space for log disks to expand to their maximum size. See log size. • When creating disk groups, plan for the impacts of DR group logs. Log size When a DR group pair is created, the size of each log disk (source and destination) is 136 MB (Vraid1), by default. The initial size is also called its minimum size. When logging, the size automatically increases in proportion to the host data written to the DR group, up to a preset maximum. By default, the maximum size is determined by the controller software. However, you can manually set the maximum. Log size example maximum size [varies] ^ ^ ^ initial (minimum) size • The actual size and the requested size of a log are reported. When these differ, it indicates the requested size change cannot be made until the log state changes. • In synchronous write mode, the log is automatically returned to its minimum size when a merge is completed or a full copy is performed. In enhanced asynchronous write mode, the log is not returned to its minimum size when a merge is completed or when a full copy is performed. • Sometimes a log can become much larger than is typically needed. In this case, HP recommends that you edit the DR group properties and make the log smaller. HP StorageWorks Replication Solutions Manager 4.0.1 105