•Update copy operation
•Read and write I/O operations for URz volumes
•Secondary data volume write option
•Secondary data volume read option
•Difference management
Initial Copy Operations
Initial copy operations synchronize data in the primary data volume and data in the secondary data volume. Initial copy operations are performed independently from host I/Os. Initial copy operations are performed when you create a data volume pair or when you resynchronize a suspended pair. The initial copy operation copies the base-journal data that is obtained from the primary data volume at the primary storage system to the secondary storage system, and then restores the base-journal to the secondary data volume.
If the journal-obtain operation starts at the primary data volume, the primary storage system obtains all data of the primary data volume as the base- journal data, in sequence. The base-journal contains a replica of the entire data volume or a replica of updates to the data volume. The base-journal will be copied from the primary storage system to the secondary storage system after the secondary storage system issues a read-journal command. After a base-journal is copied to the secondary storage system, the base-journal will be stored in a restore journal volume in a restore journal group where the secondary data volume belongs. After that, the data in the restore journal volume will be restored to the secondary data volume, so that the data in the secondary data volume synchronizes with the data in the primary data volume.
The base-journal data is stored in the entire data volume or the area for the difference. The area for the difference is used when the difference resynchronization operation is performed. The journal data for the entire data volume is created when the data volume pair is created. The difference journal data is obtained when the pair status of the data volume changes from the Suspending status to the Pair resync status. Merging the difference bitmaps that are recorded on both primary and secondary data volumes enables you to obtain the journal data for only difference. When a data volume pair is suspended, the status of data that is updated from the host to the primary and secondary data volumes is recorded to the difference bitmap.
The base-journal data of primary storage system is stored to the secondary storage system journal volume according to the read command from the secondary storage system. After that, the base-journal data is restored from the journal volume to the secondary data volume. The initial copy operation will finish when all base-journals are restored.
Chapter 2 About Universal Replicator Operations | 2-19 |
Hitachi Universal Replicator for IBM /OS User’s Guide
