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Chapter 2 About Universal Replicator Operations 2-19
Hitachi Universal Replicator for IBM /OS User’s Guide
• 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.