Note: If you manipulate volumes (not journal groups) to create or resynchronize two or more data volume pairs within the same journal group, the base journal of one of the pairs will be stored in the restore journal volume, and then the base journal of another pair will be stored in the restore journal volume. Therefore, the operation for restoring the latter base journal will be delayed.
Note: You can specify None as the copy mode for initial copy operations. If the None mode is selected, initial copy operations will not be performed. The None mode must be used at your responsibility only when you are sure that data in the primary data volume is completely the same as data in the secondary data volumes.
Update Copy Operation
When a host performs a write I/O operation to a primary data volume of a data volume pair, an update copy operation will be performed. During an update copy operation, the update data that is written to the primary data volume is obtained as an update journal. The update journal will be copied to the secondary storage system, and then restored to the secondary data volume.
The primary storage system obtains update data that the host writes to the primary data volume as update journals. Update journals will be stored in journal volumes in the journal group that the primary data volume belongs to. When the secondary storage system issues "read journal" commands, update journals will be copied from the primary storage system to the secondary storage system asynchronously with completion of write I/Os by the host. Update journals that are copied to the secondary storage system will be stored in journal volumes in the journal group that the secondary data volume belongs to. The secondary storage system will restore the update journals to the secondary data volumes in the order write I/Os are made, so that the secondary data volumes will be updated just like the primary data volumes are updated.
Journal Group Operations
URz journal groups enable update sequence consistency to be maintained across a journal group of volumes. The primary data volumes and secondary data volumes of the pairs in a journal group must be located within one physical primary storage system and one physical secondary storage system
When more than one data volume is updated, the order that the data volumes are updated is managed within the journal group that the data volumes belong to. Consistency in data updates is maintained among paired journal groups.
URz uses journal groups to maintain data consistency among data volumes.
Chapter 3 Preparing for Universal Replicator z/OS Operations |
